@Treaclewell Sorry, but I disagree with basis of your post, that assumes that everything that happens with humans is for some evolutionary reason or purpose.
Humans like all organisms are complex and something so complex can go wrong. AGP has been described as an erotic target location error, and many men who talk about it normally talk about a "gender incident" (as I call it), (typically a cross-dressing incident) in childhood which basically develops into AGP come puberty.
There isn't some sort of cultural evolutionary process that makes men AGP for evolutionary benefit, just that the wiring of the brain has gone a bit wrong.
Perhaps there is something in DNA that makes people more susceptible to developing fetishes, but cancer is also genetic and we don't claim there is a need for that or that we accept it.
I've seen a lot of women get worried about there being a genetic or biological element to AGP or even trans, because they then assume we have to accept "born this way", we don't. We as a society can place limits on behaviour, no matter how it developed.
And I in no way am claiming that people are born in the wrong body.