I don't accept that premise and I still think it's a point worth investigating. It's obvious that monogamy does make many people happy, but justifying it by an appeal to nature that isn't even true does few favors to the >50% of people who have been failed by the ideal of life-long monogamy.

What if psychopathology comes from conflict between individual idiosyncratic sexual feelings (caused by early, incorrectly locked-in interpretations of group norms?) and group norms?

It's as good an explanation as any other, I suppose. Ryan and Jetha do talk a bit about paraphilia in men, but that chapter disappointingly lacked the rigor displayed elsewhere, so I wasn't planning to discuss it.