I've come across spam/scam posts with big lists of drugs for sale.

Most relays already have things in place to block spam since patterns like "fresh npub posting the same thing over and over" are easy to pick up.

As for actual individuals, depends on what the "illegal content" is really. If it's CP there will be a shitload of reports and they'll be banned by clients and relays alike. They will also be targeted by the feds for real unless they only use Tor, same as the rest of the internet.

Stuff that's of more debatable moral value like Silk Road stuff using Nostr Market and Civ Kit is just gonna happen, also through Tor. I'm fully in support of that.

Basically the answer is it's the same as the rest of the internet.