I'm currently working at a pretty small company with women coworkers, and most of them are at least as smart as some of the men i've worked with and one is way smarter than most people i've met. Having said that, in my experience both in college and at work (been working about 6 years now), on average the girls were less capable and smart at CS and programming. From my experience it seemed A LOT like they just didn't commit at nearly the same level as the guys. For most men who are programmers it's almost a way of life - I have never met a woman for whom the same could be said. The one woman I know who is vastly better at her job than anyone I've met, even she is simply a extremely dedicated professional for whom it is just a job, not truly a passion.
I'm not saying this means guys get the right to be assholes, I'm just saying I don't think this is entirely because there are so few girls or because of stereotypes, i think there is more to it than that, there is a statistically discernible difference in skill - from my limited personal experience. Please proceed with the downvote into oblivion :).