It would be fully okay to have relays with local moderation rules. See nostr as a connection hub of multiple forums into one feed, and that's how it kind of works.

One must just make sure to be picky when choosing relays. Today the variation of relays aren't large enough, but the selection of more moderated relays will grow, I'm sure of it.

Client side it doesn't make much sense to implement much more than ignore, mute and block. But Relays could implement ban and complex spam & moderation algorithms. Someone just got to do it.