Error messages are not hidden. Many of these policies are never communicated, not even in error messages. That's when people get angry and the operator's reputation goes to the trash.
Discussion
Communication goes a LONG way towards user experience. If you're running a service, tell your users what they can and can't do. Relying on non technical people to figure out what they're able to do is a bad user experience. Nostr benefits as a whole when users have better experiences.