All fandoms are going to have their more extreme fans claiming that certain characters are the best, this season is the best, or the show was ruined when they did this, etc. I am part of the Lion King fandom and there is a divide between hate/love/indifference to The Lion Guard. Even worse would be Kopa from The Lion King Six New Adventures. There are so many threads whether he's cannon or not. Anime can get pretty fanatical as well even though I am an otaku. I think it's fairly rude to say "Oh, you only watch that show, you're not a true fan!" In anime there's the sub vs. dub debate. Subs have gotten better since the days of DBZ and Sailor Moon, but I still prefer subtitles because I feel it is more accurate and I get more of an authentic feel. However, some people are dub fans, and I'm okay with that (I'd recommend staying away from some like Sailor Moon and Cardcaptors mainly because of how horribly they're done).
Even pet ownership has its radicals. If you don't feed your pet a certain food or follow a certain type of diet you are setting your pet up for health failure, are an irresponsible owner, etc.