I think one of the hardest things for people in tech to admit is that an uneven gender ratio is by itself a deterrent to talented women considering the profession. You can say that people shouldn't care about same-gender mentors and co-workers, etc, but at the end of the day, people care about fitting in and they don't want to have to ride against the current their whole career. A bright young woman considering law school, where she'll be in a 50-50 environment, or engineering school, where she'll be in a 20-80 environment, has a natural disinclination to choose the latter.