The reason a fandom gets hate because there's a mole within the fandom. The reason why everyone bashes on each other is that a fan from that fandom is so toxic and isn't sensitive yet to realize the situation for example:

BTS ARMY (disclaimer i'm not using this very fandom to opinionate each of their personalities)

when an ARMY says this: "bts is like king and boss of the whole wrold or whatevs" IMMEDIATELY another fandom or any other random person opinionates on them and eventually
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it effects tho whole public image of the fandom which creates other opinions and for this thread/case, Hate/rs.