Fascism, racism and qanon are all black and white "not cool". Communism and anarchism are much more nuanced schools of thought.
Absolutely there are extremists from all parts of the political spectrum. I guess my point is that being communist in itself is a part of the spectrum. There are undoubtably parts of it I'd consider extremist. But the only place I've seen anything that extreme was on lemmygrad, which has thankfully been defederated by nearly everyone. lemmy.ml is the largest instance I'm aware of that still federates with them.
I look at in different terms. If the more moderate members of a group (lemmy.ml), stop engaging with extremists (lemmygrad).. the extremists will be stuck in an echo chamber with no stabilising influence.
I genuinely hope you are right that moderating influence can out-influence the echo chamber. I really don't want Lemmy to go the way of 4chan. Here's hoping!
Where are the self described anarchist devs? I've only seen self described communism (and censorship of criticism of authoritarian governments on dev run instance.)