Just to be clear I'm not saying relays or Damus or whatever have to do moderation on every possible category that someone somewhere might want to moderate. Only that there are certain minimal levels of moderation that are required by law.

Relays need to comply with the laws where their server is located and where the owner has a business presence (or where they're a resident/citizen if it's owned by an individual).

Damus and other iOS apps have to comply with Apple's rules - which are based primarily on US/EU law. That might change somewhat when Apple introduces support for other app stores. But given that it's the EU mandating that change I can't imagine those app stores will be legal free-for-alls.

And I'd add that anyone that runs a web client on their domain has to comply with certain laws as well or they also risk problems. They can be sued, they can be charged with crimes, their domain can be seized.

It'll be interesting to see how it all plays out legally. I expect you're going to hear the Client apps/applications say "that's not my data - I got it from a bunch of relays - in fact most of those relays were chosen by the user - not by us". Meanwhile the relays will say "I didn't present the information to the user. I gave it to the Client app/application - it was the Client's job to figure out what to present and what to ignore." There are some really interesting legal questions presented by Nostr…

You don't want to be the guy who gets sued or prosecuted first. Lawyers are expensive. Let someone else be the guinea pig.