@pluralistic A game theory explanation of this, that I read a while back, is that communities play a complex version of the iterated prisoner's dilemma - which has a very successful strategy of being nice to people unless they're shitty to you - but as the community grows it devolves into an independent series of simple prisoner's dilemmas (which have a dominant strategy of being a dick) as the proportion of repeated interactions between individuals drops. So this is why big subreddits are toxic but small ones retain community. Community schisms are also super interesting - Zachary's Karate Club being a canonical example.
