Real life is the biggest echo chamber you'll ever find. Online is one of the most diverse spaces you'll find. That said there's nothing to be gained by humoring fascists, ML, or groups only interested in engaging in bad faith. I say this as someone who trends social libertarian and is always up for some Marxism.
I do think real life can be an echo chamber, but if you have a diverse range of people you interact with, it can be not an echo chamber at all. Having multiple friend groups, attending social events, etc can make real life more diverse.
(Ofc there's things like living in a first world country making an echo chamber of people that don't care about third world issues, but that's beside the point)
No one ever gets radicalized in these cases, hearing the same things from everyone they interact with thinking that everyone or at least most think the same way they do and they need to fix the situation while being encouraged to do so. Never happens.
All I'm saying is that defedding from people like "tankies, alt-righters, edge lords" are fine, but because it's easy to miscategorise people into those categories (intentional or not) you could end up defederating from anyone you don't agree with, ending up in an echo chamber.