You are a serf in someone’s serfdom in Fedi-bro-verse.
On nostr, no one can ban you from nostr.
Discussion
But I can create my own server on fediverse, like a nostr relay. There's no ban mechanism on a nostr relay server?
Correct.
The key difference is that on nostr your keypair is not attached to the server of a single despot, or benevolent dictator.
You can readily change your nostr relay list.
Oh, so it's like in running over servers and I can change them on the fly?
Check out my relay list pictured on nostr:npub18m76awca3y37hkvuneavuw6pjj4525fw90necxmadrvjg0sdy6qsngq955
Most nostr apps allow you to modify your relay list.
Go to nostr.watch for a directory. Also check out nostrpul.se both created by nostr:npub1uac67zc9er54ln0kl6e4qp2y6ta3enfcg7ywnayshvlw9r5w6ehsqq99rx 
Also be sure to check out mostr relay by nostr:npub108pv4cg5ag52nq082kd5leu9ffrn2gdg6g4xdwatn73y36uzplmq9uyev6
This is your fedi-bro-verse to nostr bridge