The very sad, unfortunate thing is that a lot of these authors are indeed mentally ill. A lot of the ring-leaders of these mobs openly embrace their mental illness as a personality trait (ie: listing it in their Twitter bios).

It leads to this bizarre environment where their reactions are, medically speaking, insane (ie: the reaction of someone in bipolar mania, the reaction of someone suffering from paranoia or extreme anxiety.) But there are so many insane reactions, that it becomes normalized.

And then people who don't struggle with mental illness start to mimic the insane behavior, because hey, everyone else is doing it! And it's now the best way to get internet points, collect followers, and get some profitable attention to your own books.