There two ways to define what kinds of excuses "should" be "valid" for a given behavior: the deontological way (like the "ick" reaction in your comment), and the consequentialist way (how will people's behavior change if society deems such-and-such excuse "valid").

Now the deontological way has a big drawback: it's impossible to argue intelligently about, as you have aptly demonstrated with the penis references and whatnot. Different people have different deontologies. Without adopting some flavor of consequentialism, we can never have a rational common ground to say that your deontological standards are "better" than mine, and everyone leaves with their opinions unchanged. This is why I prefer to start from the opposite side: try to evaluate only the consequences of icky decisions, not how awful their descriptions sound. It also helps check that my deontological instincts aren't lying to me.

Is it true that you (a rationalist person, possibly american) would accept jealousy as an excuse for murder?

cousin_it wasn't moralizing one way or the other. He was suggesting game theoretic incentives not targets for righteous blame and shame.

Incidentally in some cultures such a policy would be appropriate. Particularly those in which:

• individuals have the responsibility for protecting their own rights rather than being able to and obligated to rely on the state interfering for them.
• Genetic paternity tests are not available and customary.

Cuckoldry is a serious economic and social violation. Much like the other types of violation that people may need to challenge each other to duels over. Increasing the severity of the consequences of getting caught decreases the need for paranoid supervision.

Seriously, this reminds me of a group of 13 years old finding out whose penis is bigger to enrage those of shorter size. It is way too childish to pass unnoticed here.

This comment struck me out of place.