Adultery should be a crime

[Autolykos]

I refer you to Wikipedia for a list of benefits spouses in the US enjoy through marriage. They are quite substantial.

Sorry, I wasn't aware that you intended the scope of this thread to be specific to the United States. Nothing in your OP suggested such. Certainly the wording of point #1 in the OP made it seem as though you were speaking in general terms about the institution of marriage, and not about some specific legal implementation thereof (US or otherwise).

With that said, I ask again: what do you think are the benefits of any given* marriage contract?

(* Note: By "any given" I mean not tied to the US or any other particular government/legal system.)

The distribution of assets from a divorce depends on numerous factors, and is further subject to its own particular set of rules.

I take it you are (again) talking specifically about the current US laws? If so, we have a serious context problem. Again, your wording in the OP seemed to indicate to me that you were speaking in a general or hypothetical sense; i.e., your arguments were not tied to any particular government or legal system.

A contract is simply a mutual agreement between two or more parties. It stands to reason that, if one party breaks the terms of the contract, the other parties can seek compensation. What other factors may determine the compensation seem irrelevant to this point.

If we deem adultery harmful enough, then we cannot allow its penalties to be contingent on divorce settlements alone.

Why is that, exactly? Explain to me how that is not a non sequitur.

Secondly, you must be using an exclusive "we" there, because I would certainly not be a part of it.

I thought it should be obvious. If you, as a child, found out that your father was having sex with someone other than your mother, how would you feel? Also, how would you feel if your parents' relationship is soured because of this?

That would depend on whether I already believed adultery is wrong (which would depend on whether I knew about it at all), and how my mother would react if/when she found out about it.

Based on your response, it seems you did not mean physical harm, but "psychological harm", which seems to me a very nebulous concept. I would still like to know what you mean by "tearing apart families". Until you give me your (personal) definition, I must take it as a glittering generality.

AIDS remains one of the top killers in the world, and numerous other STDs are still quite potent, such as HPV which can lead to cancer.

Accidents are also one of the top killers in the world, and otherwise quite potent.

Furthermore, just because something is not "the most harmful thing out there" doesn't mean it isn't harmful. By your reasoning, since thievery is not as harmful as murder, we shouldn't outlaw thievery.

Wrong. Your third point, as I understand it, expressed the following syllogism:

1. Adultery bears the potential for spreading STDs.
2. STDs are a form of physical harm.
3. Therefore, adultery bears the potential for physical harm.

It also implicitly expressed an additional syllogism:

1. Things which bear the potential for physical harm should be considered crimes.
2. Adultery bears the potential for physical harm (from above).
3. Therefore, adultery should be considered a crime.

Now, substitute "driving" for "adultery" and "car accidents" for "STDs". I don't think you will see any incompatibility here.

Your analogy fails because my case against adultery is not contingent on the potential harm of STDs alone. I have shown that adultery is akin to reneging on a contract. I have also shown how it devalues an important social institution, and how it is viewed as immoral.

Your other arguments against adultery are irrelevant here. In effect, you seem to be arguing above that your third argument against adultery must be true because your other arguments against adultery are (presumably) true. This is something of a fallacy of distribution, don't you think?

Finally, driving serves the important purpose of transportation. Adultery serves no such purpose. When considered in combination with all its demerits, there is a case for it to be criminalised.

Some people would consider sex to be a very important purpose, even more important than driving. Importance is not an objective, empirical phenomenon, except in the sense of "Person X thinks that A is more important than B but less important than C."

You misunderstand what fallacies are. The above are only fallacious if I use them to support an objective truth claim. I am making no such truth claim. My claim is that adultery should be a crime, which is a normative one.

There are a few ways to respond to this:

1. You seemed to be implying the argument that, because many or most people view adultery as immoral, it is immoral. Likewise, because many/most people have traditionally viewed adultery as immoral, it is immoral. Finally, because committing adultery can have presumably negative consequences (as a result of many/most people viewing it as immoral, among other things), adultery is immoral. Note that none of this has any impact on the normative proposition "Anything immoral should be illegal."
2. That proposition runs into the is-ought problem. One can get around this by rewording the proposition in goal-oriented terms: "Given the goal of eliminating immoral actions, making immoral actions illegal will (help) eliminate them." Hence, normative propositions can conceivably be discussed using logic, and thus logical fallacies can apply to them.
3. Otherwise, if logical fallacies cannot apply to normative statements, logic in general cannot apply to them. However, this also means that one cannot turn around and (try to) defend or justify normative statements using logic, for he would be engaging in an apparent performative contradiction.

When determining what acts should be crimes, public moral sentiments are very important, and the moral culpability of an act has always been an important consideration in the crafting of our laws.

What makes public moral sentiments "very important", exactly? How do you think one can determine the moral culpability of an act?

My personal view is that these acts should not be criminalised, but that is irrelevant to this topic. They were brought up as examples to support the viewpoint that acts can be criminalised solely on the basis of moral repugnance; there is a legal precedence for that.

This seems again to embody an appeal to tradition. It also begs the question as to whether there is a difference between repugnance and immorality.

Adultery is not only morally repugnant but also harmful. Why shouldn't it be criminalised?

One reason I can think of is if those of State impose a particular definition of marriage (and thereby adultery) upon everyone, whether they personally agree with that definition or not. Add to this the idea that agents of the State, as implicit third parties to everything, can bring charges upon people even when no one else wants to.

In such a situation, what we could call the "real" parties to a marriage contract -- husband and wife -- could mutually agree to change the terms of the contract (e.g. allow for extramarital sex) after the initial agreement, yet agents of the State could still prosecute the adulterous (in their eyes) party.

This would arguably ruin the marriage in question more than the extramarital sex, putting the agents of the State in a position of a performative contradiction, albeit weaker than that embodied by, say, destroying a village in order to save it.

Point 1, where I argued that being able to commit adultery without criminal sanctions cheapens the institution of marriage, which is an important unit of social organisation. In order to reinforce the notion that marriage is sacred, stiff penalties should be levied on those who stray.

Okay, thank you.

I would define adultery as deliberate sexual contact with someone other than your spouse. This includes mutual masturbation, oral, anal and vaginal sex.

So a man who, while not partaking in your definition of "adultery", leers at other women constantly and views pornography obsessively can also cause considerable grief upon his wife and children, yet his actions would be considered legal by you. On the other hand, a man who, by mutual agreement with his wife, engages in occasional extramarital sex is committing a heinous and illegal act, in your opinion.

I am thinking of fines, and possibly short periods of imprisonment.

Fines go to the State. Restitution goes to the victim(s). Perhaps you are implicitly arguing/assuming that the State is a victim? If so, please affirm and justify this position. Otherwise, because fines enrich the offices of the State, there is no economic incentive for agents of the State to prevent or otherwise eliminate adultery. There becomes, however, an economic incentive for them to ensure that adultery, if it seems at all likely to occur, will occur, so that the State's coffers will be that much fuller.

Thus, agents of the State will be motivated to let adultery occur rather than take measure to prevent it in the first place, due to some amount of dependence on fines received from successfully-prosecuted adultery cases. As far as I can see, this is an inversion of "destroying a village in order to save it", but no less of a performative contradiction.

[GoldPhoenix]

Disclaimer: I am aware that some countries and states in the US do list adultery as a crime. However, the law is seldom enforced and is non-existent for all intents and purposes. Also, there are many other countries that don't make adultery illegal. Thus for the purpose of this thread, assume that adultery is legal at the moment.

In this thread, I propose that adultery should be made illegal. Here's why:

1) Adultery undermines marriage. When a couple gets married, they typically undertake an oath to stay committed to each other till death. The act of adultery is against the spirit of the vows the couple undertook, and cheapens the institution of marriage. If we see marriage as a legal contract, it is preposterous that people are allowed to enjoy the benefits of a contract without having to uphold its terms and conditions. By outlawing adultery, it would make marriage that much more sacred and not something to be entered into lightly.

2) Adultery, if found out, can also tear apart families, often harming children in the process. If we cherish our family values, if we want to foster a healthy environment for our children, we ought to outlaw adultery.

3) Adultery bears the potential for physical harm. If a spouse (let's assume it's a male) has unsafe sex outside of marriage, he may contract STDs and spread it to his unwitting wife. We all know that the best way to prevent the spread of STDs is not contraception, but monogamy and fidelity.

4) Adultery is overwhelmingly viewed as immoral, be it by secular or religious people.

5) (Related to #4) We outlaw many other acts that are viewed as immoral by fewer people, and don't even pose any demonstrable harm, such as necrophilia and bestiality.

So, we have here an act that has all of the following elements - the breaking of a contract (figuratively speaking), harm to individuals (the spouse, the children), harm to society at large (by undermining a cornerstone of social organisation), and moral culpability. Can someone tell me why it shouldn't be outlawed?

Because putting people in jail for adultery just doesn't make sense.


Adultery is a wrong against a wife or husband, and since (as Zhavric says) 3 does not hold water, there's no reason why it should not be handled by the wife and there's no reason why the government should get involved.

[mican333]

In this thread, I propose that adultery should be made illegal. Here's why:

1) Adultery undermines marriage. When a couple gets married, they typically undertake an oath to stay committed to each other till death. The act of adultery is against the spirit of the vows the couple undertook, and cheapens the institution of marriage. If we see marriage as a legal contract, it is preposterous that people are allowed to enjoy the benefits of a contract without having to uphold its terms and conditions. By outlawing adultery, it would make marriage that much more sacred and not something to be entered into lightly.

2) Adultery, if found out, can also tear apart families, often harming children in the process. If we cherish our family values, if we want to foster a healthy environment for our children, we ought to outlaw adultery.

3) Adultery bears the potential for physical harm. If a spouse (let's assume it's a male) has unsafe sex outside of marriage, he may contract STDs and spread it to his unwitting wife. We all know that the best way to prevent the spread of STDs is not contraception, but monogamy and fidelity.

4) Adultery is overwhelmingly viewed as immoral, be it by secular or religious people.

All of these fail for the same reason - that none of them are criteria for outlawing something and to outlaw adultery based on them would either require extremely selective enforcement or outlawing an endless number of things that obviously should be illegal.

1. Undermines marriage. Shall we outlaw everything that could undermine marriage?

2. Tears families apart. Shall we outlaw everything that could ruin a marriage?

3. Spreads STDs. Sex in general, not just adulterous sex, spreads STDs. Outlaw sex?

4. Public opinion. Outlaw everything the public doesn't like?

[starcreator]

I think Mican did an excellent job of summarizing the problems with this argument. One can make the case that adultery is bad, which is all well and good, but there is no causal link between something being bad and socially harmful and its being illegal.

First, there are the exceptions that many have raised to the implicit rules of legality you invoke. There are many contracts that are not legally enforceable, like promises between individuals, even though breaking them may cause harm to third parties. Divorce may harm children, but we don't outlaw it. Non-exclusive fornication spreads STDs, but we don't outlaw it. Finally, under a liberal democratic state, we permit many things that are widely held to be immoral; necrophilia and bestiality are the radical exceptions to this rule, not the precedents upon which we should build future legal codes.

The burden lies with Trendem to demonstrate why existing precedents of law, under each subcategory, must be violated in order to admit this new circumstance.

[Apokalupsis]

btw, according to the USMC (US Military Code), adultery is illegal and is punishable. Just thought I'd throw that in there for discussion.

[CliveStaples]

The burden lies with Trendem to demonstrate why existing precedents of law, under each subcategory, must be violated in order to admit this new circumstance.

New? If I recall correctly, adultery was, at one time, a crime. Other private consensual acts have been criminalized--Texas outlawed consensual homosexual sodomy. There's plenty of legal precedence to suggest that adultery could be made illegal; I'm just not convinced that it should be.

[mican333]

New? If I recall correctly, adultery was, at one time, a crime. Other private consensual acts have been criminalized--Texas outlawed consensual homosexual sodomy. There's plenty of legal precedence to suggest that adultery could be made illegal; I'm just not convinced that it should be.

As the OP said (and I haven't confirmed it to be true but I will take his word for it), there are laws on the books in some states outlawing adultery but they aren't enforced.

And I'm guessing if someone did try to enforce it, it would go to the courts and likely be shot down for the same reason the laws against consensual homosexual sex are no longer enforceable - the belief that private consensual sex is private.

[CliveStaples]

As the OP said (and I haven't confirmed it to be true but I will take his word for it), there are laws on the books in some states outlawing adultery but they aren't enforced.

And I'm guessing if someone did try to enforce it, it would go to the courts and likely be shot down for the same reason the laws against consensual homosexual sex are no longer enforceable - the belief that private consensual sex is private.

Whether or not it is private, the fact would be that it is against the law. I think that Lawrence v. Texas, which struck down Texas's anti-sodomy law, was wrongly decided. I imagine that you are correct; anti-adultery laws would probably be struck down on the same wrong basis.

[mican333]

Whether or not it is private, the fact would be that it is against the law. I think that Lawrence v. Texas, which struck down Texas's anti-sodomy law, was wrongly decided. I imagine that you are correct; anti-adultery laws would probably be struck down on the same wrong basis.

You don't agree that there is a right to private consensual sexual activity under the right to privacy? Such a right was recognized back in 1965 in Griswold v. Connecticut.

Lawrence just said that it applies to gays as well.

[CliveStaples]

You don't agree that there is a right to private consensual sexual activity under the right to privacy? Such a right was recognized back in 1965 in Griswold v. Connecticut.

Lawrence just said that it applies to gays as well.

First, the right to private consensual sexual activity was based on jurisprudence about "fundamental rights", which by definition are "deeply rooted in our nation's history and traditions". So far as I can tell, homosexual sex has not been "deeply rooted in our nation's history and traditions"; there have been laws against it in many states for many years. So I don't think that particular justification works.

Second, insofar as rights applying to gays, homosexuals enjoy exactly the same rights heterosexuals do. If there exists a fundamental right to homosexual sex, then heterosexuals enjoy that right as much as homosexuals do.

[mican333]

First, the right to private consensual sexual activity was based on jurisprudence about "fundamental rights", which by definition are "deeply rooted in our nation's history and traditions". So far as I can tell, homosexual sex has not been "deeply rooted in our nation's history and traditions"; there have been laws against it in many states for many years. So I don't think that particular justification works.

But Lawrence vs. Texas says that to apply the right to straights but not gays is a violation of equal protection of the law and I really don't see how it could not be.

You're going to punish gays for doing something that you allow straights to do?

Second, insofar as rights applying to gays, homosexuals enjoy exactly the same rights heterosexuals do. If there exists a fundamental right to homosexual sex, then heterosexuals enjoy that right as much as homosexuals do.

It's not the right to a specific sexual act with a certain person, but the right to privacy which covers ALL private consensual adult sexual activity.

And saying "except for gays" is certainly denying gays equal protection of the law.

[CliveStaples]

But Lawrence vs. Texas says that apply the right to straights but not gays is a violation of equal protection of the law and I really don't see how it could not be.

The law applied to both homosexuals and heterosexuals; any person, regardless of sexual orientation, was disallowed from engaging in consensual sodomy with someone of the same gender. Just as both the rich and poor are disallowed from stealing bread.

You're going to punish gays for doing something that you allow straights to do?

Straights were not allowed to engage in consensual sodomy with a person of the same gender.

[mican333]

The law applied to both homosexuals and heterosexuals; any person, regardless of sexual orientation, was disallowed from engaging in consensual sodomy with someone of the same gender. Just as both the rich and poor are disallowed from stealing bread.

Heterosexual sexual activity is recognized under the right to privacy. What makes homosexual activity so different that it can be denied the same recognition?

[CliveStaples]

Heterosexual sexual activity is recognized under the right to privacy. What makes homosexual activity so different that it can be denied the same recognition?

The fact that it is not "deeply rooted in this nation's history and traditions", thus is it not a "fundamental right". It may be safely made the object of criminal statutes--unless and until a Constitutional amendment is passed, either on the state or federal level, to the contrary.

[mican333]

The fact that it is not "deeply rooted in this nation's history and traditions", thus is it not a "fundamental right". It may be safely made the object of criminal statutes--unless and until a Constitutional amendment is passed, either on the state or federal level, to the contrary.

Show me an clear LEGAL definition of what is and is not "deeply rooted in our traditions". Not your opinion, but the actual working legal definition and how it is suppose to be applied.

And either way, it is NOW recognized that gays and straights are legal equals so even if there is "deeply rooted tradition" of discriminating against gays, it is no more. In recognition of that, there cannot be laws that discriminate against gays and deny them equal rights.

[CliveStaples]

Show me an clear LEGAL definition of what is and is not "deeply rooted in our traditions". Not your opinion, but the actual working legal definition and how it is suppose to be applied.

And either way, it is NOW recognized that gays and straights are legal equals so even if there is "deeply rooted tradition" of discriminating against gays, it is no more. In recognition of that, there cannot be laws that discriminate against gays and deny them equal rights.

The laws do not discriminate against gays; both straights and gays alike are equally subject to the law.

The legal definition of a "fundamental right" is one that is "deeply rooted in our nation's history and traditions". Does homosexual sex fit that definition? Please be specific.

[mican333]

The laws do not discriminate against gays; both straights and gays alike are equally subject to the law.

The legal definition of a "fundamental right" is one that is "deeply rooted in our nation's history and traditions". Does homosexual sex fit that definition? Please be specific.

The right to privacy is a fundamental right deeply rooted in our traditions and it covers ALL private consensual private sexual activity.

[CliveStaples]

The right to privacy is a fundamental right deeply rooted in our traditions and it covers ALL private consensual private sexual activity.

So homosexual sex is "deeply rooted in our nation's history and traditions"?

[starcreator]

New? If I recall correctly, adultery was, at one time, a crime. Other private consensual acts have been criminalized--Texas outlawed consensual homosexual sodomy. There's plenty of legal precedence to suggest that adultery could be made illegal; I'm just not convinced that it should be.

There is little precedent that has been upheld in modern criminal law. Most of the arguments used to support adultery (such as society considering it immoral) are predicated on precedents which have been superseded by new principles (given that all sorts of things are legally permissible that people consider immoral).

So homosexual sex is "deeply rooted in our nation's history and traditions"?

No, the right to privacy is deeply rooted in your nation's history and traditions. Private homosexual sex is simply the natural implication of the right to privacy; enshrining the latter while prohibiting the former presents a contradiction. It is among the roles of the judicial system to compare law with enshrined, fundamental rights and strike down law that violates them.

[Trendem]

There are still way too many respondents for me to reply to all personally, so I'll be doing another thematic response, and only reply individually where the rebuttals raised cannot be easily summarised.

1) Each and every one of the points in the op, can be made to oppose the idea of gay marriage.
Claiming it doesn't make it so. Please demonstrate how gay marriage entails the breaking of vows, harm to third parties, etc.

2) The government should not have the right to interfere in marriages
Again, no support has been given for this assertion. Since marriage is very much a legal institution, conferring legal benefits, the government HAS the right to interfere in it. You cannot expect to have your cake (legal benefits) and eat it too (free from government intervention). If you disagree with the illegalisation of adultery, then get a divorce, but continue living with your ex-wife.

To summarise, the moment you choose to get married, is the moment you have decided to take your relationship out of the "personal" sphere into the social and legal sphere, where the government has a valid interest in intervening.

3) If adultery is outlawed based on certain factors, then other acts that share those factors should be outlawed too
This is a very simplistic way of viewing things. Every act has its own benefits and drawbacks. Also, there are practical considerations to whether we can criminalise an act or not. Thus, when determining whether a particular act should be a crime, we need to evaluate it holistically. Take the example of driving, which many people have brought up. Sure, driving may cause accidents, but it is currently an indispensable aspect of transportation, and if we outlawed driving, our entire economic system would break down. Thus, to make it a crime would be absurd.

4) What about spouses who mutually consent to having an "open" marriage?
As stated above, you don't get to have your cake and eat it too. Marriage is meant for people who want to stay committed to each other, not for people who want to derive the legal benefits of being committed to another person in name, while enjoying the pleasures of extramarital sex on the side. If you disagree with a fundamental cornerstone of marriage, which is fidelity, then you shouldn't get married in the first place.

But regardless of that, the fact remains that adultery would be chiefly reported by unhappy cheated spouses. If a couple has no problems which each other having affairs, then none of them would be punished. In my envisioned model, the police will not pro-actively investigate if people are committing adultery or not - they will only act when a report is made.

5) The marriage contract is not legally enforceable
The whole point of this thread is to discuss whether or not the terms and conditions of marriage (more specifically the aspect of fidelity) should be more official and binding, so as to increase the sacredness and seriousness of marriage as an institution. Stating that marriage vows are currently non-legally binding misses the point thoroughly.


_________________________________ _{Post Merged} _________________________________

Sorry, I wasn't aware that you intended the scope of this thread to be specific to the United States. Nothing in your OP suggested such. Certainly the wording of point #1 in the OP made it seem as though you were speaking in general terms about the institution of marriage, and not about some specific legal implementation thereof (US or otherwise).

That is indeed true; I directed you to a list of benefits couples in the US enjoy as an example of marital benefits, not as an authoritative list.

With that said, I ask again: what do you think are the benefits of any given* marriage contract?

The benefits, IMO, are chiefly legal and economic benefits such as tax deductions, extension of employment benefits to cover your spouse, etc.

I take it you are (again) talking specifically about the current US laws? If so, we have a serious context problem. Again, your wording in the OP seemed to indicate to me that you were speaking in a general or hypothetical sense; i.e., your arguments were not tied to any particular government or legal system.

Divorce laws in most developed countries are rather similar, so I'm not tying my arguments to a particular jurisdiction. Are you disagreeing with the fact that the distribution of divorce assets are contingent on numerous factors other than the act of adultery by one party?

Why is that, exactly? Explain to me how that is not a non sequitur.

How is it a non sequitur? You made the claim, you support it.

Based on your response, it seems you did not mean physical harm, but "psychological harm", which seems to me a very nebulous concept. I would still like to know what you mean by "tearing apart families". Until you give me your (personal) definition, I must take it as a glittering generality.

Adultery is one of the primary reasons for divorce. Divorce leads to the separation of husband and wife, and the distribution of children among the two. Need I elaborate more on what constitutes "tearing apart families"?

Where adultery does not lead to divorce, it also causes feelings of betrayal and distrust, creating a schism between husband and wife, which may take a long time to heal. While the damage may not be as extensive as a divorce, it still poses a significant negative impact on the family.

Wrong. Your third point, as I understand it, expressed the following syllogism:

1. Adultery bears the potential for spreading STDs.
2. STDs are a form of physical harm.
3. Therefore, adultery bears the potential for physical harm.

It also implicitly expressed an additional syllogism:

1. Things which bear the potential for physical harm should be considered crimes.
2. Adultery bears the potential for physical harm (from above).
3. Therefore, adultery should be considered a crime.

Now, substitute "driving" for "adultery" and "car accidents" for "STDs". I don't think you will see any incompatibility here.

As stated previously, you misunderstand my argument. I'm not saying that adultery should be considered a crime based on its potential for spreading STDs alone. By isolating that as the sole reason for criminalising adultery in your syllogisms, you have constructed a straw man of my argument.

Your other arguments against adultery are irrelevant here. In effect, you seem to be arguing above that your third argument against adultery must be true because your other arguments against adultery are (presumably) true. This is something of a fallacy of distribution, don't you think?

You are once again mistaken. At no time did I state that my third argument is true because my other arguments are true. My third argument is that having unprotected sex outside of marriage bears the risk of spreading STDs to your own spouse. The fact of this argument stands on its own - the risk of spreading STDs is increased by infidelity and multiple sexual partners. But this argument, in itself, does not constitute a sufficient reason for criminalising adultery.

Your rebuttal of this argument has always focused on its sufficiency, not on its truth. If you want to consider sufficiency, then you of course need to consider all my arguments as well.

Some people would consider sex to be a very important purpose, even more important than driving. Importance is not an objective, empirical phenomenon, except in the sense of "Person X thinks that A is more important than B but less important than C."

Nobody is proposing that people should be disallowed from having sex. The proposal is that if people want to derive the benefits of marriage, then they need to stay faithful to their spouse and have sex with them only. If an individual places great importance of having sex with multiple partners, then he shouldn't get married in the first place - for a cornerstone of marriage is faithfulness.

There are a few ways to respond to this:

1. You seemed to be implying the argument that, because many or most people view adultery as immoral, it is immoral. Likewise, because many/most people have traditionally viewed adultery as immoral, it is immoral. Finally, because committing adultery can have presumably negative consequences (as a result of many/most people viewing it as immoral, among other things), adultery is immoral. Note that none of this has any impact on the normative proposition "Anything immoral should be illegal."

First of all, I am not saying that adultery IS immoral. I'm saying that adultery is viewed by the public as immoral, which is what matters when determining the law. As a matter of fact, I believe that morality is a social construct, and that no act is objectively moral or immoral.

The first chapter of any criminal law textbook would tell you that a key element of a crime is moral blameworthiness, and moral blameworthiness is chiefly determined by public sentiment. As Lord Justice Denning - whose views greatly shaped the common law - wrote:

...in order that an act should be punishable it must be morally blameworthy.

Sir John Barry of the Supreme Court of Victoria also wrote:

It is... true beyond question that in the reality of the social process an important end of the criminal law is to reinforce and uphold the moral sentiments of the community that favour the promotion of virtue and discourage the pursuit of evildoing...

(The above quotes are culled from Smith and Hogan on Criminal law, Fifth Edition, pp. 4 & 7)

This is not to say that law textbooks and the views of past jurists must be correct. But for the purposes of this debate, we have to agree on this conception of crime, especially since it is the prevailing one in most countries.

2. That proposition runs into the is-ought problem. One can get around this by rewording the proposition in goal-oriented terms: "Given the goal of eliminating immoral actions, making immoral actions illegal will (help) eliminate them." Hence, normative propositions can conceivably be discussed using logic, and thus logical fallacies can apply to them.

Yes, as you noted, it depends on how my argument is worded. But how exactly did I word my argument? You seem to be straying far from the original context. Here's a recap:

Me: Adultery is overwhelmingly viewed as immoral, be it by secular or religious people.

You: I think this is at least an appeal to tradition, if not also an appeal to consequences.

You intimated that it is an appeal to tradition to state that adultery should be outlawed due to public sentiments, which is a misapplication of fallacious theory. A fallacy of an appeal to tradition only occurs when someone uses it to justify a factual claim, such as this:

God exists because throughout history people have always believed in God

My argument was more of the following:

Criminal laws are established based in part on public moral sentiments.
Adultery is overwhelmingly viewed as immoral by the public.
Thus, this is a factor in favour of criminalising adultery.

Where is the logical fallacy?

3. Otherwise, if logical fallacies cannot apply to normative statements, logic in general cannot apply to them.

False, because as you yourself noted, it is possible to phrase normative statements in objective, syllogistic forms, thus rendering them amenable to logical disputation. Your mistake consists in applying logical fallacy theory to normative statements directly, without taking time to decode them into positive syllogistic form.

What makes public moral sentiments "very important", exactly? How do you think one can determine the moral culpability of an act?

Please see above regarding the basis of criminal law. The question of WHY public moral sentiments are important in the establishment of laws is out of the scope of this discussion; you just have to accept that it is currently the foundation of our laws.

This seems again to embody an appeal to tradition. It also begs the question as to whether there is a difference between repugnance and immorality.

You ought to stop indiscriminately applying logical fallacies. It is a common misconception by people who have a superficial understanding of fallacies that whenever someone appeals to tradition to justify something, anything, it must be wrong.

An appeal to tradition is wrong in cases where tradition has no bearing on the truth of a claim. But in the case of the law, legal precedents (i.e. "tradition") is an important component. There is no error of reasoning here - the unspoken premise is that the precedents are an important consideration when formulating the law.

One reason I can think of is if those of State impose a particular definition of marriage (and thereby adultery) upon everyone, whether they personally agree with that definition or not. Add to this the idea that agents of the State, as implicit third parties to everything, can bring charges upon people even when no one else wants to.

In such a situation, what we could call the "real" parties to a marriage contract -- husband and wife -- could mutually agree to change the terms of the contract (e.g. allow for extramarital sex) after the initial agreement, yet agents of the State could still prosecute the adulterous (in their eyes) party.

This would arguably ruin the marriage in question more than the extramarital sex, putting the agents of the State in a position of a performative contradiction, albeit weaker than that embodied by, say, destroying a village in order to save it.

Please read my above remarks about marriage being about faithfulness, and how one cannot have one's cake and eat it too. Unless the majority of society turns against this conception of marriage, there is no reason for the government to change the definition and spirit of marriage. People who want to engage in relationships contrary to the spirit of marriage shouldn't get married in the first place.

So a man who, while not partaking in your definition of "adultery", leers at other women constantly and views pornography obsessively can also cause considerable grief upon his wife and children, yet his actions would be considered legal by you. On the other hand, a man who, by mutual agreement with his wife, engages in occasional extramarital sex is committing a heinous and illegal act, in your opinion.

Our laws are neither perfect nor comprehensive. While it would be ideal to tackle all instances of wrongdoing that lead to marital dysfunction, the fact remains that it is often impractical to do so. Instead, the law seeks to target more significant acts of wrongdoing. Thus, run-of-the-mill lies are not criminalised, while fraud and defamation are.

Fines go to the State. Restitution goes to the victim(s). Perhaps you are implicitly arguing/assuming that the State is a victim? If so, please affirm and justify this position.

First of all, the objective of fines in this case is not restitution, but punishment. Secondly, I have made the case that adultery transgresses against society in general by undermining a key social institution - marriage.

Otherwise, because fines enrich the offices of the State, there is no economic incentive for agents of the State to prevent or otherwise eliminate adultery. There becomes, however, an economic incentive for them to ensure that adultery, if it seems at all likely to occur, will occur, so that the State's coffers will be that much fuller.

This reasoning is exceedingly specious. For one, it conflates the enforcers of the law with the recipients of the fines. The economic incentive for enforcers to prosecute adultery is the same incentive they have for prosecuting any other crime - it is within the scope of their job, on which they depend for a livelihood. They do not receive the fines which are obtained through successful prosecutions of adultery.

Second, it makes the unjustified assumption that "agents of the State" can actively prevent adultery (other than via criminalising and prosecuting adultery), and thus require incentives to do so. What exactly do you have in mind?

Third, even if we assume that "agents of the State" would zealously prosecute adultery in order to enrich the state's coffers, you neglect the obvious fact that the very enforcement of the law would pose a deterrent effect on the act.