Jeff Crews, current President of Splat Space from this article:
Q. How can we encourage more women to participate in hackerspaces?
A. Stop being a**holes. It's that simple, but I'll expand on it. The ownership of breasts, ovaries, and/or uterus is irrelevant to the ability to think logically, plan a project, present ideas clearly, use mathematics, code, solder, fabricate, or do anything else that might be going on in a hackerspace. (It becomes relevant only if and when a female member decides to do some bio-gyno-hacking on herself so that she can bear a genetically engineered baby-superweapon. That isn't an issue yet.) It is as irrelevant to hacking as is the social construct of "race" or someone's genetic makeup/ethnic background.
Women, like everyone else, want a welcoming and comfortable environment. An African-American potential member would probably look askance at a hackerspace that flew the Confederate battle flag. Likewise, a weekly rape joke competition would create what is known as a "hostile environment" for potential female members.
It's a delicate issue, especially since hackerspaces are often home to people who espouse various libertarian/Objectivist/anarchist/radical honesty philosophies, who see this as an assault on free speech. What those people don't realize is that those philosophies and the willingness to employ them usually come from a position of enormous privilege and safety that not everyone shares. Curbing one's tongue to make others feel more comfortable isn't censorship, it's courtesy. It's also good business for any organization.