Here's how I see it, and anyone else who disagrees is free to disagree:
People have trouble explaining how things were done well. If they are good reviewers, they will try to do this anyway (and I've come across a few who will admit they're nit picking when their nit picking) so how come so many don't? Consider these observations:
- Everything has flaws.
- That's the nature of most people- to point out those flaws.
- Everybody has different ideas of what exactly is a flaw, leading to the conflict.
- Unless the fandom has made a conscious decision to respect each other's opinions, it can get ugly pretty quickly.
- In the cases of the poisonous fandoms you seem to be referring to, all joy is lost in bickering and fighting. Knowing all this stuff, what can we do about it?
Really, the only thing we can do is just enjoy what we enjoy. It's difficult when so many people decide to be negative, but most people are fans of things because they like them. It's natural to want more or to dislike change, but in the end, the only person you really control is yourself.
Personally, I avoid negative fandoms, or if a fandom is large enough, focus on the aspects of it that make me happy. I don't let arguments about this kind of stuff get me down; I tried to discuss it mainly with people who have respected my opinions in the past. And I make a decision to try to respect people's theories even if they differ from mine.
The arguing about all the pairings in some fandoms (I think someone further up uses Sonic as an example) actually helps me write more well rounded fan fiction, and if there's something that I'm legitimately uncomfortable with, I just ignore it. Although it's a pain when you run across that.
There's good things and bad things about being a fan, but it's your choice which you focus on. I'm a natural optimist, but you still have to practice it.
(and I'm using "you" in a general sense here.)
Animaniacs made a sketch about extreme fandom.