What right do they believe to have to dictate to their users what the can and can't read? That should be solely in the user's hand.

Are they choosing what people can read, or are they choosing what they're willing to federate? No one is stopping people writing and publishing things on federated services. People are only choosing what they're willing to broadcast over the part of the service they run.

Yeah, I also don't understand their take. HN also dictates what their users can and can't read. There's tons of stuff that can't be posted here without being removed. That's a good thing.

Exactly. Each instance is deciding who to federate with and each user is deciding which instance to join