I've seen it in several forms of fandom. I recently left one of my favourite FaceBook groups, a football group, because of the negativity, the namecalling and general abuse. Ironically, it was a group set up with the intended aim of being a pleasant and safe place, different to the others. The guidelines, paraphrased, were to not be too negative, criticise players, and to have a good time. That was great for a number of years, and then it grew too large. And when people pointed out the guidelines, they were attacked for their rose-tinted glasses, and reminded of the abuser's right to "free speech."
I'm only in one Science Fiction group, run by a friend, which is still small and where people are nice to each other. (I've only had to block one person who insisted I was wrong, and actually commented on my post "What he actually means is....", which is not what I meant. But apart from him, it is a fun place to visit. I stopped going to others when it was insinuated that we weren't allowed to enjoy certain films, or books, because they were rubbish. Like many of the Star Wars films, or series, or books.
I left a music one because people would go out of their way to declare their hatred of all things U2, a band I quite like. it was bizarre how these people were on a mission to let you know they didn't like them.
At the moment, there are a number of Beatles fans already declaring they don't like the new Beatles song, even though none of them have heard it. It's not the Beatles, it's not this, it's not that.
Negativity. I'm cutting it out of my life where I can. And my Facebook feed is a much happier place for it.