This is definitely a strength of federation.

Want to get rid of right wing communities and their fascist members? Defederate with the instances that host them.

Want to get rid of left wing communities and their commie members? Defederate with the instances that host them.

Want to get rid of hate communities and their toxic members? Defederate with the instances that host them.

You don't need to completely close communities, you can just let people have those discussions in their own space, as should be their right. Centralised systems don't really have this choice.

I think this too. Let them have their little corners of the internet so they stay away from the rest of us. If they want to use public spaces to talk about fucked up stuff and type up their plans like idiots, well, all the more reason to make it easier for watchdog groups to keep track of them. I think we should keep the upvote/downvote system. Maybe once a comment (or post) reaches a certain number of downvotes, it gets marked as hidden, instead of censored or deleted. That way the users can self-mod along with the mods. I don't think there's a need to tally votes outside of each individual comment/post, so we can get rid of karma which is nice

It’s going to be a challenge for them to reach new people to warp to their worldview if they are largely kept away from everyone else.

This only makes sense if you assume that new people would be funneled into extremist Lemmy instances from other Lemmy instances, but it's far more likely that new people will be pointed toward such communities through other paths, and then they won't be exposed to competing ideas.

Don't misunderstand me - I'm not saying that hate speech, racism and sexism should be ignored or allowed to exist alongside other content on Lemmy. I am saying that trying to ignore that, separate ourselves from it, and pretend like it doesn't exist and doesn't affect us, is ultimately counterproductive.

The problem with letting things fester is that they tend to grow and get worse while they're out of sight/out of mind, until they eventually burst out and spread toxicity everywhere.

One of the benefits of free speech is that the nasty stuff gets exposed. When it's exposed then you at least know where it is. The only problem is if the nasty stuff doesn't get labeled as such so it can be dealt with, and instead is treated as if it were normal and allowed to continue spreading (e.g. police turning a blind eye to far-right gun nuts intimidating voters).