I used to use usenet at my girlfriend's house and they were completely uncensored... every illegal topic imaginable, pictures, movies, everything. It was a bit scary. That was how I found out about how crazy the world is. Anyway, is it censored now or is all that stuff still on there? And is it as massive as it was (1996) or more so, or less so?
Think of NNTP like SMTP (which are very similar is design) -- only people pass around news postings instead of e-mail. And instead of e-mail being distributed from originating server of the From: field to destination server of the To: field, the posts stay on that server, and then are bulk transferred as the "newsgroup" to other servers that "subscribe" to its feeds.
The only central piece is the owning server of the newsgroup. But even then many things are proxied/cached, etc... by end servers, core subscribing and other servers. So it's even more decentralized than it was 15 years ago. There is also the legal precedents that a distribution system is not responsible for content it does not generate itself, which then gets into (at least in the US context) of Freedom of Speech v. Copyright law. So far, probably because so few people know about the UseNet anymore, no real focus has been made to regulate it.
About the only copyright enforcement done is on an individual basis by the copyright holders themselves. E.g., if your ISP requires you to login to post a message and will not allow you to post anonymously, and you post pictures from ... say ... Danni.COM, you'll find yourself quickly making some legal considerations.
But no, if you're into various, illegal things from the standpoint of US law -- with many of these newsgroups being based outside the US -- it's not regulated. Unless, of course, you're an American citizen who is physically caught with that stuff on your computer -- which has little to do with the newsgroup. Thank God I'm not into that stuff.
But I'll freely admit I can't get enough of curvy goddess women intimate with men, so I hit UseNet frequently. I have at least 50GB and probably 50+ hours of stuff I've downloaded that I haven't even sorted through yet and just haven't gotten around to.