How this is related with the source of the content?
How do you (not) stop them today with Twitter o Facebook? Same thing.
Nostr goal is not to avoid content stealing, but at least, as Fiatjaf said, "with signed messages they cannot misrepresent what you're saying".
If I want to grab all of your tweets, say, don't I have to be approved for API access, some process that they control in some way, and that they can shut off for the bad actors?
An API is of course the "official way".
But it is only a matter on time/energy, you can always do web scraping using an extension o a bot.
A lot of copycat sites and content farm sites today are built up in this way.
As soon as the content is online you cannot prevent it from being copied.
