Except, they dont have all of the messages. Most people post to the 10+ top relays. 

Besides they are blocking thousands of sites - automatically. It's absolutely zero effort for them to block a few extra relay sites every day.

anon

If a government blocks one relay by firewalling its IP, you can just switch to others. There are hundreds of public relays worldwide, and they're constantly popping up. Your private key ensures your identity and data stay yours, no lock-in to any relay.