That's the reason why classes for girls (not necessarily primarily but directed towards) work so well. Being in a room full of men with few or no women in ANY circumstance is awkward unless you are top of your game.
On the other hand, "foo for women" events are high-pressure environments that put a spotlight on poor newbies. It's a way of saying "You aren't just here to learn something, you're representing women, you're here to prove something for all of us". It implies that the mainstream groups aren't safe or okay places for women to learn. Additionally, they prevent those newbie women from learning the social scripts and memes that will help them fit in with mainstream hacker culture (or even programmer culture), so they get to be total outsiders as juniors instead of as freshmen, which really sucks.
I sincerely doubt it, but feel free to prove me wrong.
The team of psychologists examined all available research on single-sex education published within the past seven years, which included 184 studies comprising 1.6 million students from kindergarten to 12th grade in 21 different countries, and found no evidence to support proponents’ claims.
In their study, which appeared Monday in Psychological Bulletin, a journal published by the American Psychological Association, the psychologists said that students who attended single-sex schools weren’t any better off than peers who attended coed programs in terms of self-esteem or performance in STEM (science, technology, engineering and math) subjects."
http://america.aljazeera.com/articles/2014/2/5/study-single-...
I've never really cared, whether I'm at the top or bottom of my game. Biological sex of the people around me is irrelevant--unless I'm going to a gay bar.