A relay can only prevent me from posting to their server but they can't stop people from viewing content I host on my own relay server or stop users from finding the content on other servers.

"Clients can connect to whatever relays they want. Clients aren't married to any individual relay, they can grab events from dozens of relays at a time. Events stored at one relay can even point to events stored at totally different relays."

I'm currently connected to 20 relays, 6 or so paid and others free. As running your own relays become easier and easier, nostr will become increasingly decentralised and censorship-resistant. It's already possible to run your own private relay on rumble.