This article by a female sceptic is worth looking at. The author, Rebecca Watson, is one of the main writers on Skepchick.org. She's very active - a big fan of Randi, critical thinking, etc. etc. - and always assumed that she was part of the same community of likeminded folk. That is, until one day she took the men gently to task for hitting on women at sceptic conferences. Cue a tidal wave of misogynist abuse. Then Richard Dawkins weighed in with an extraordinary comment on Pharyngula and all hell broke loose.
Watson has now stirred the pot with this much fuller article on Slate.com. It gives an interesting slant on the sceptic movement, and is worth a read. I'd be surprised if there wasn't a lot of discussion about it, and about what it means to be a sceptic.
It's not just sceptics who behave badly online, obviously. But they seem oddly prone to it.