This is not a modern phenomenon, nor is it one limited to horror fandom. It’s endemic in all fan communities, and is, ultimately, part of the very nature of community; there is no meaningful inclusion without exclusion. Status comes from tromping on someone else, on forcing a hierarchy. I think the best answer is to always push for a more sophisticated discourse, to always make the argument for the unpopular opinion, to always keep the discussion fluid. When someone wants to draw a line in the sand, let the winds of conversation blow it gently away.