>>203014444Many different reasons for many different people.
Some have developed the retarded edgy mentality that being "angry", whiny and "jaded" is somehow "fun" or "satisfying", so they try to top each other in negativity. They tend to look for fanbases big enough to let them argue a lot. So it's shitposting, in short.
Others feel some kind of childish and one-sided rivalry for other popular series. They're weak people that lack any sort of individuality so they feel the need to attack they're "rival" series, because they see their popularity as a personal attack to themselves: they need their taste to be "objectively" correct to feel safe. If they come to think that they can't manage to bend the general opinion over these trivial things, they start to throw tantrums. It's something that shares its nature with salesfaggottry.
There's also the mediator, another weak kind of person that can't form his own opinion if not relatively to others'. You'll see them always choosing a middle ground, no matter what they truthfully think. It's not an harmful behaviour unti the discussions are civilized, but as soon as the two categories above start their routine they become just as harmful to the quality of the threads, since they try to rationalize irrational points. They're kind of like the people who don't like some series because they don't like the threads.
All of these categories share a common factor: popularity. The more popular something is, the more likely it is for threads to be overly negative and terrible for discussion.