Re. Mastodon: Insular communities gonna insulate. Defederation has collateral damage, but among some communities that is acceptable because they view intolerance and the toleration of intolerance as close enough to warrant blanket handling. (See that "Nazi bar" story that's often cited)

Re. Lemmy: I think we will see much of the same. Lemmy is (IMO) in a slightly more immature state than Mastodon was when it had one of its early booms (when I ran an instance briefly). Especially w/r/t mod tools and stuff, which is part of why things are fragmenting at the moment.

I want my instance to run "under the radar" for the most part. Personally I'd rather leave things up to individuals to decide what they do or don't want to see. For example, if you enable NSFW content and browse "all" posts, don't be surprised if there is NSFW content there. Or content you don't agree with. But, if you borrow my car with my company logo on it (use my instance) to go to someone else's house (some community on another instance) and piss in their cornflakes (break that community's rules) I am not going to let you keep borrowing my car (kick you off my instance). And on the communities fully hosted on the instance itself I want them to generally be welcoming to others, which includes showing people who are not welcoming the door.