IMO it has to do with people needing validation online. The more people that agree with them, the more they think that their way of thinking is right and just. They then shift to communities and people that don't point out the fallacies in their views which is colloquially called an "echochamber". Then it just snowballs into this sort of subculture or tribe that foams at the mouth any time someone comes along with a different opinion which creates overly dramatic situations like this that would never occur in the real world, but people like to put their internet armor on and draw their ego swords thinking their entire way of life is being threatened because someone says something like "Why are you so agressive to these other people?"