Women (and some men) tend to be very suspicious of male-only spaces because they think that said men are plotting to reestablish the Patriarchy. Not really, though.

Sometimes it's nice to have a safe space where you don't have to police yourself for the opposite sex and risk being misunderstood by them. I don't begrudge women their own space, and I would hope that women, feminist and otherwise, would not begrudge men theirs.