I used to think this was only a property of algorithms but I'm not convinced anymore. Any number of link aggregator sites I'm on with no algorithmic surfacing of content, Reddit (at least on the old site), HN, Lobsters, Tildes, etc all have the same effect. Everyone comments on and engages with the rage inducing post. Nuanced, sanguine conversations get maybe an upvote or two but are just a few posters talking. This tracks with my experience on forums back in the '90s where huge hellthreads would spawn and have people arguing for weeks, and every archive of Usenet flamethreads that I've seen.
I don't think the algorithms are helping, but I think this is just a property of socializing in the large. Humans, when socializing in person, have a lot of context. When my friend rants "relationships are terrible they are just adults emotionally manipulating each other" to me, and I have the context of knowing my friend just had a bad breakup, I know the place this is coming from. When someone posts this on Twitter, everyone is up in arms because there's no context. There's other properties of socializing in the large that I suspect leads to the patterns we see in online discourse, but I'm beginning to think that the algorithms are the minor part.