Absolutely block instances hosting illegal content - the way federation works means copies / caches of content can end up on this server? Or even if that’s not how lemmy does it, it risks using this server to facilitate the spread of something incredibly harmful & damaging.

As far as I’m concerned there’s no argument for allowing / normalising content produced which quite literally ruins peoples lives.

Edit: Even stuff that’s purely cartoonish in nature for me is just grim, and I don’t want to be a part of a community which supports it.

Edit2: If a server can block a specific community posting CSAM then maybe that's a better solution than blocking the underlying infrastructure. If that's not possible, I think defederation is the only real way to deal it, as frustrating as that would be for legitimate users.