I mean, to some people it's just natural--how else do I react to a story besides saying what I thought about it?

Yes, that's pretty much me. The thing is, I don't really want to talk about fic I didn't like, but I do want to talk about stories I like. I'm actually more likely to point out the flaws of something I consider well written than of something I consider crap - the latter just isn't worth the effort to me. So to me, really, concrit is the highest compliment I have to give to a story, and I get frustrated if people take it as an insult instead.