Unless I'm mistaken, Facebook is not a government and ignorant, uncivilized people getting whats coming to them features heavily in his works. While he certainly frowns on censorship, people intolerant and incapable of behaving themselves are usually thrown out an airlock or otherwise completely ejected from society to roam the surface Mars alone. If you're going to argue the Heinlein route, perhaps Holocaust Deniers need some frontier justice instead?