Well, Nostr does have private messages.
The issue with private messages is that everyone can still se who is sending a private message to whom, at what time and how long.
The only private thing, which not even relays can see, is the content of the message.

My point was that Nostr isn't very dissimilar respective to your direct control of things that you publish (not just send to others privately): whatever you use, others may use that content in any way, including illegally. It's not really something you can technically prevent.