Honestly I don't think an algorithm needs to work very hard to "be mean" like that. Sure, you can purposely put people with clashing views in each other sight on a place where people go to hang out and have fun. But you don't even need to go do that on purpose. To some extent, people naturally produce more "engagement" with stuff that's controversial/argumentative.

Imagine if I were to walk past you and say some completely innocent comment. Now imagine I were to walk past you and insult your favorite movie/show/song/game/whatever. You'd be far more likely to respond in the latter case.

So, as people respond, more activity is generated, and that makes the post "hotter". Simply boost what's hot, and you have a veritable litany of controversy.