It's cultural, otherwise there wouldn't be any of them left.

I would argue the people susceptible to cultural nonsense to the point of delusions and self mutilation are inferior specimens not fit to reproduce.

We barely have real natural selection anymore, this is natures way of removing the unfit in an environment with rare natural deaths. See Calhoun's studies on the rats he made gay in a similar environment (plentiful resources, crowded living spaces, i.e. urbanites of some privilege, like cities in the US)