Relay operators can choose to censor. Deleting/blocking notes is not something the protocol doesn't allow. If the relays do not want to moderate, its on them. Any court would agree that hosting pedo content is illegal and they won't be able to hide behind the "it's a protocol" thing.
Discussion
Same applies to the apps though, if the apps allow access to illegal content then the apps are also liable. Which means ultimately the apps end up having to either apply censorship themselves before it reaches the browser or they have to only operate on nodes with censorship.
At that point, what's the benefit of the protocol, other than being a really slow way to send information?