Bannability is similar to lemmy. Each "instance" (or "relay" in nostr words) can decide what content/users can live on their relay. The difference is that you are usually connected to multiple relays. So if you want to follow somebody who is banned by other relays, nobody can take that choice away from you. Likewise, nobody can stop you from publishing, though your reach may be limited by relays sharing blocklists etc.

There are some right users there just as there are on any social media network. You can just click block and move on and/or pick relays with stronger moderation policies. If Lemmy has a "left" tilt, Nostr has a "libertarian right" tilt. But over time it's expanding and becoming more generalized, just like how Lemmy isn't 100% tankies now.