Whenever you get a large group of people together to discuss a common interest, and people are passionately interested and emotionally invested in the thing being discussed, it is absolutely inevitable that irrational behaviour will go on, flamewars will erupt, trolls will emerge, and before long the entire fandom will be dismissed as a bunch of wacked-out morons who seriously need to Get a Life.
The key to surviving in any fandom is to find a group of people who, even if they don't necessarily agree, are at least mature enough to handle disagreement sensibly. This can be difficult if a large percentage of your fandom is hormonally crazed and/or ON CRACK, but with a little searching and effort, it can be done. Then you stick with the sane people and ignore all the other stuff.
See? Much better.
No, this rant was not inspired by HP fandom. Though you can apply it there too if you like.