I think Lemmy is and will be quite good at remaining civil because the questionable content makers use their own instances and get defederated. The most edgy community federated with the main cluster I found is !funhole. It features cryptic posts that presumably make sense if you engage in the decentralized (IRC? Telnet??) discourse channels of sdf.org and some appear to be pro-fascist depending on how you interpret the questionable veil of sarcasm. I don’t think it’s serious enough to consider defederation because the worst ones get massively downvoted anyway.