Mastodon is perfect for affirmation of your worldview and strengthen your social bubble because instance rules are intolerant to random kind of opinions.
You are correct that since nostr is censorship resistant, you can't really prevent someone from posting something, but you can prevent being exposed to it on your side.
If it's a single nostr account (npub) sending you something you don't want, then you can block or mute them (the blocking is done in your app on your device). If they try attacking you at scale, then you can rely on web of trust (i.e. only allow content from people you actually follow, and 2nd degree) - this is now often the default.
That works for our own account to avoid seeing the texts, it doesn't prevent the troll from still posting replies to our posts.
With that said, that is an exotic situation. I'm a big fan of NOSTR in overall, all my recent hobby projects used npub and nsec. The simplicity and power of that combination is really powerful. No more emails, no more servers, no more passwords.
