I think the answer is pretty complex and gets into why online communities in general become hostile, not just Reddit.

First off, there are incredible amounts of money and effort being spent to make people feel tribal and hate each other. Destabilization happens by convincing people that those next to them are at fault for their woes, and ensuring they don’t look up at the strings being pulled.

Second, those who generally aren’t hostile naturally don’t gravitate to places that are, so the gravity of hostility increases by hostile people being there and echoing hostility to those they perceive to be being hostile to them, even if the sentiment is “be less hostile.” It’s baked into meme culture. “Touch grass” is genuinely like “hey go outside, take a breath” at its core, but is now an insult or hostility that gets a reaction of further hostility.

Third, the world is really fucking shitty in ways outside of most people’s control. You can vote, martyr, donate, but generally the world has gotten to a close point to 100s of sci fi stories we’ve written warn us about, and so some people are just doing what the money in item one is spending, the conditioning works. Feels warm to hate someone. But then for those on the opposite they want to hate what they consider stupid.

That being said, people are genuinely shitty often, and it’s foolish to pretend that’s not the case. Open source has often been full of pettiness and bickering. Many a GitHub threads are just arguing about someone who wants a feature and is mad at volunteer developers for not delivering it. I could go on a tirade but I’ll end there