I think there is a conflation between enforcement ("How can I stop this") and ethics ("Should be we doing this").  You cant stop racism, but you can call it out.  Definitely on nostr there are those that will want to post exclusive content on relays THEY choose.  Perhaps a community relay, like a facebook group relay.  I'm saying that data ownership should be respected, and people own their own data.  You might not be able to stop it, but you can call it out.  We have a web of reputation and trust already.  Things like "antizaps" (negative zaps) are going to be quite important to call out bad actors.