once the extremist bubble is big enough, if you just let them interact with the rest, they can spread a lot of toxocity and do a lot of damage which you also want to avoid

Yeah, 100% agree. There is a benefit to free exchange of communication, it is one of the most effective ways of tearing down authoritarian structures, but absolutely at the same time once it's interfering with your own quiet enjoyment and ability to communicate internally it might be time to shut it out. I actually sometimes just don't participate at all in the political communities on lemmy.world for exactly that reason; it is often so toxic that it shuts down even the ability for people to have a normal conversation. Such a noisy tide of people will emerge to exercise Lemmy Reading Comprehension and give random hostility that you can't hear the other calm people. That's also the issue with Hexbear. That whole event where one of the more permissive instances thought about refederating with them, and they immediately brigaded that very discussion post to hurl abuse at everyone and so the conclusion was "lol never mind," is a good example.

There's also an important factor of whether the people in the community you're talking to are open to change. Lemmy.ml seems obviously to me to be mostly genuine people who are on some level interested in conversation and care about these topics, which is one reason I lean towards keeping engagement with them even if sometimes is a ridiculous conversation. But at the same time, I don't really fuck with Hexbear or with UniversalMonk much, because it just doesn't seem that there's much to be gained. If someone's whole overarching goal whenever they interact with outsiders is going to be "doing a bit," then what's the point. You're just the cat playing with their little toy-on-a-stick because they're waving it around, at that point.