These are Americans exercising their constitutional rights to freedom of speech and assembly. Whether you agree with the protestors or not is irrelevant. Your rights are impacted, too, by this arbitrary platform bias. This cannot stand for long. We have to move away from centralized monopolies on the web.
Facebook is not a public entity; they are a private company and the Constitution does not constrain it. You can argue that Facebook is depriving you of your Constitutional rights until you're blue in the face, but it'll probably get you nowhere in court.