acv on Nostr: The problem isn't that people shouldn't share the note with other relays, it's that ...

The problem isn't that people shouldn't share the note with other relays, it's that they could and inevitably would. The note is self-authenticating, if it's valid, if it's Nostr. The server isn't the database of record, or anything. If it's read by someone other than you, it can be shared and instead of it being someone just claiming you said this, it would be as if you said it yourself, and all of Nostr would accept it as valid and authored by a public key.