Are you talking about people who act out on their fandom by criticizing others? "Oh I'm a fan of X, therefore I'm a vocal critic of Y". I agree that such things are toxic -- fandom doesn't need to be a polemic.
I want to cultivate the kind of fandom that builds up without feeling a need to tear down others.
Most people are "oh that's fun to watch ok" and then when they don't like it anymore, they get bored and forget about it entirely.
The anti-fans continue to follow it, but rabidly hate it.
Think Syndrome from Incredibles. He's always been the biggest fan.