I live in Arizona. When someone cuts me off on the freeway, my instinctive response is to look at the license plate. If the license plate is from a northern state, my reaction is "Fucking snowbirds. Goddamn." I'm in my car, and I'm just reacting - I'm not thinking. Five seconds of thought calms me down, but until that happens, I'm making a pretty nasty comment about the elderly.
The Internet is similar to my car - it's a consequence-free space where people can just say things without thinking. The difference is that unlike my car, where I could spout off the worst racial profanities I can come up with, the Internet actually has people reading the posts.
As for Internet communities being devoid of women, I can think of exactly one general community that has women. It has three things that I think are vital - a small community, a draconian moderation team, and a userbase that calls out bullshit very quickly.