The problem I see is taboos assume the act is always wrong, and preclude consideration for edge cases where it might be the lesser wrong. Consider the incest taboo--yeah, there are very good reasons for this. Should you enter a sexual relationship with a relative? I think society is better off prohibiting this. But what about "What, my wife is actually my sister????" Is forcing them to divorce actually the best answer? (And, yes, it happens. Bump into an unknown sibling, there's a substantial chance you'll fall for them.)

The only thing wrong with incest is the child. We put a lot of focus on this but not other kinds of ‘bad’ genes like hereditary diseases.

To me taboos is just society taking shortcuts. This is fine, but lets admit that we are taking shortcuts.