If relays won't accept your content, it will have a very difficult time spreading. However, every relay makes the decision independently, so it's not a blanket ban from the network. That said, relays may use automated systems, so a number of relays using the same software with similar configurations may still automatically act in unison and hit a content creator hard.
Discussion
So it's pretty much "freedom of speech doesn't mean freedom of reach". Seems like theres always a control mechanism. Someone destroys the whole selling point of Nostr. Brutal
That's always been true everywhere. You have the freedom to speak, not the freedom to force people to listen to you. Relays are free actors, and it's unreasonable to expect them to host and propagate content they don't wish to support. Any relay that wants to allow a free for all can simply not enable any sort of automated moderation. You can even spin up your own relay so nobody can silence you entirely and any who wishes to listen to you can always get updates from you there.