With fanfic, I think..it has a lot to do with the fact that we know we are playing with the forbidden, so much of fanfic is sexual fantasy, something the outside world scoffs at and makes fun of. That we can't tell people outside of fandom about. So...because of that, people are itchier and more nervous.
It's almost more personal in a way, than ordinary fic is. Or at least that's been my impression.

I have the impression that the new generation of fans is more tolerant to critique. After your notes on one the recently posted fics I had an exchange with Angearia about it. I wrote that I'd be thrilled to read your concrit, even if you'd critisize me harshly - I'd be like "OMG, she reads my stuff!" Angearia replied that her reaction would be the same. And it was sincere. Not that I think that you'd read and critique my stuff - I write silly OOC stories and I'm the first person to tell you that they're not worthy of serious critical analysis.

But I've got the impression that recently many peoplу are okay with concrit. Back in 2005-2006 there was a concrit community
http://community.livejournal.com/ficconcrit/profile
it's pretty inactive now, but maybe we should try to revitalize it?