To clarify, I mean in-real-life, in-person discussion groups, not online.
I know a group in Cambridge had some trouble recently with male members insisting on 'playing devil's advocate' and talking about how feminist issues were oppressing men(!). That's the type of thing that I'd be wary of. However, there are of course plenty of men who are perfectly capable of intelligent discourse around feminist issues without being misogynistic twunts. Why shouldn't they be welcome?
It boils down to this: Should feminist discussion/activism groups be women-only, or should men be allowed?
Personally I am very conflicted on this, so am really interested to hear all your thoughts on it :)