Late to the party but keen to add my penn'orth.
I'm a long time lurker and occasional poster and LOVE the feminism section of MN. It's a bit upsetting/tedious to find us having this discussion, but I think some useful reflections are being posted.
My experience is that the tension most often arises on those threads that address some of the fundamentals of feminism and it happens because of a mismatch between what people regard as 'opinion'.
To take rape as an example - experienced posters and long-time feminists accept as fact that incidents of rape are not affected by what the victim is wearing - there is plenty of evidence for this. But someone who's new to the forum, or who hasn't really thought deeply about the issue or just doesn't KNOW, might believe that there is still room for shades of opinion about this. So they post their innocent opinion that women should be careful about what they wear. And typically the response to that is not 'I respectfully disagree with your opinion' but 'No, actually, you are WRONG, and here's the reason why'. The person who posted the 'opinion' then either realises their mistake and thinks more deeply about their position, or retreats into defending their position and blames the responder for being 'mean'. Other posters can then form the impression that there's no room for discussion on the feminist boards, or that only one opinion is allowed.
I agree with Beachcomber - that often people take the latter course because to acknowledge some of the 'facts' that feminists take for granted, is actually a deeply uncomfortable process, which you have to be open to. I always value dittany's (and others) contribution to debates, because they are so uncompromising. I've got to a place where I'm comfortable with exploring the logical conclusions of feminist thought and not being frightened by the implications, but I can really sympathise with those who find it threatening. Equally, it's not up to the feminist posters to make the message palatable to those who find it hard to accept.
But it could possibly help to recognise when different posters are treating fact as opinion and vice versa and tailor our responses accordingly.
BTW - wanted to acknowledge MRJhasleftthebuilding's post from earlier. Think it made some incredibly valuable points but got lost in the exchange.