Let me begin by apologising for my absence over the last couple of weeks. Christmas, New Year etc. etc.
Anyway, the matter at hand.
A man's natural desire to cheat is not justification for infidelity, and I shall show this in the following debate. I shall do this by breaking the argument down
Raw urges are routinely kept under control
You know when you see a hot girl that you fancy? Do you rape her? Because I don't, and you probably shouldn't if you do. However, rape is not inherently an unatural thing. Rape is a social construct. It doesn't exist elsewhere in the animal kingdom, because consent does not exist elsewhere. Humanity has constructed norms by which it lives and not raping people is one of them, fundamental in just about every culture. Humans are not predisposed not to rape, that's why rapists exist, but it is a choice that is made.
Almost as fundamental is the idea of monogamy. While going against the idea of monogamy is perhaps viewed in a better light than going against the idea of not raping people, the same ethical framework applies. Monogamy is a social construct, and the rules by which we choose to live our lives apply. We choose to live in this society, so we must also take its social constructs. If you want to rape people, there's little you can do about it. If you want to be polygamous, then don't enter a long term relationship. It is a choice to follow urges, not a predetirmened necessity.
"You can't always get what you want"
Mick Jagger, a man who looks like a dinnerlady but slept with supermodels, said it first, but that doesn't stop it being true. In many ways, I believe that this topic is quite descriptive of societies tendency to head towards instant gratification no matter the cost. Put simply, it implies that because a man wants to cheat, he should be entitled to do so.
The whole thing ignores the bigger picture. What about his significant other? Women have an instinctive desire for their partners to be monogamous, and an instinct to leave partners they don't trust. The reasons for this are fairly obvious and easy to see, but thus we have a vicious cycle of logic-defying shitness. If the man is entitled to cheat, as per his instinct, then the woman is entitled to leave him, as per hers, in which case the whole shebang hasn't been logically justified at any stage in the proceedings, thus nullifying the whole topic.
If it was a Cartesian one man world, then the actions of an individual can be justified by their desires and nothing else, but as soon as you bring other people into the equation, things cannot be so easily swept under the rug.
History
The historical argument is basically a melding of the two previous ones, and is very simple. Society's norms are built around biological and environmental necessities throughout time. For example, the meat restrictions within Judaism and Islam are almost certainly a result of hot temperatures and meat generally mixing to form an unpleasant brown liquid in your tunic. Similarly, we educate our youth because historically that is the way to preserve them.
Monogamy's reasons may be less obvious than those, but for whatever reason every single one of the world's most advanced civilisations practice it. This shows in beautiful simplicity why it is not an acceptable argument to say that infidelity can be explained away. Put simply, if it was in the interest of humanity to let infidelity slide, then it would not be such a taboo in every major civilisation.
And finally...
I'd like to finish this post by looking at a point my opponent made:
A person can commit murder but can use insanity as an excuse. He can be born with the mental issues the same way a man is born with desires. It should be carried over to marital problems so the same way a insane person goes to help so should a cheating man. He can then face his desires and break the addiction if it reaches that point.
The problem with this of course is the issue of choice. Somebody can plead insanity because it means that they had no control over what they are doing. A sane minded man with sexual desires has the choice to do the deed or to respect his relationship. This choice is what stops desire from being an excuse. Remember, arguing that a man cheating on his wife "because he wanted to" is essentially absolving anyone for responsibility for any of their actions, and is essentially routed in strict determinsim, an area of philosophy most people find uncomfortable. In which case, a man's actions needn't be justified at all.
