From the comments to this post, Mark Lafue’s quite reasonable comment:
I am perhaps groggy and not thinking clearly, but are there ways in which freedom of speech is protected by laws not derived from the constitution? There are and always have been laws that protect rights to property, life and liberty from non-government actors, but off the top of my head I can’t think of any that cover freedom of expression.
And my response: There are laws that Mark is not thinking of, such as international treaty laws that protect freedom of expression, but my point is to separate the idea of “freedom of speech” as a right with the laws passed to protect that right. Rights – in the constitutional sense – are not created by the laws. They exist independently, and the laws are there to protect them, not to establish them. That’s why the First Amendment reads, in part, Congress shall make no law “abridging the freedom of speech.” Freedom of speech already existed; the amendment is just forbidding Congress from trying to do away with it.
It’s perfectly possible to say “Even though the Constitution does not cover it, I believe that my freedom of speech is abridged when [insert non-governmental body] stops me from saying something.” The example I thought of as I wrote this was arbitration clauses that require the parties not to say anything. If the government was doing it, it would run afoul of First Amendment protections. That a private body was doing it (and thus escaped that Constitutional issue) does not mean that the right to freedom of speech is not being abridged.