Yeah, I think that's what at the heart of it for most of it. By no means does anyone really hate JKR (at least I don't.) She created one of the most immersive and addicting worlds out there. The only problem is that I grew to like it so much I got really let down when she would mess up or didn't write it to what I thought was the best of her ability.

I also don't really think fanfiction and canon are comparable. Without canon there wouldn't be fanfiction, and canon gave authors a chance to see what they did and didn't like and then work from there.

 

There are some communities (a few yahoo groups and the like jump to mind) that do hate JKR. For various reasons, but sometimes for the simple reason of not having Harry and Hermione up together ("After HBP, I refused to read the last book! The series is ruined!"). Petty, but for a while DLP seemed to hate Ginny, although at least we've (mostly) matured past that.