This argument is insidious, because it's extremely difficult to document a pattern, particularly when folk come out of the woodwork to undermine each and every individual anecdote claiming sexism (as in this and every other thread like this on HN. Even, I would point out, in cases where the sexism is undeniable to any rational observer).
Do you have to believe every anecdote? Of course not. Should you let those women have a voice to air their perceived grievances, without stifling them in the name of "fairness" or "defaults"? To do any less is the very definition of institutional sexism.