Radicalization happens through words. You can ban radicalization by banning words.

That won't completely get rid of it, but it can make it a lot less accessible, which reduces the amount of radicalization that occurs. I don't think people start out with the intent to get radicalized. They stumble upon a place like /pol/ and see that it's interesting and so they stick around and gradually get convinced. It's much harder to stumble upon a Tor hidden service or a private chatroom than a publicly accessible webpage.

China's great firewall is not terribly hard to get around, but it's very effective regardless. Inconvenience is powerful.