Then your definition of Free Speech is something different from the one generally agreed upon and implemented in many constitutions. You can look at it that wa

Then your definition of Free Speech is something different from the one generally agreed upon and implemented in many constitutions. You can look at it that way: If a private entity is prohibited from deleting user content, isn't that also an infringement of free speech? And at what level are they prohibited to filter such content? Are they allowed to require an account? Are they allowed to delete spam? No "Right to Free Speech" can be enforced between private persons or entities. Nobody can be forced to listen to you, nobody can be prohibited from taking measures to not read or hear you, just because you claim a right to free speech. Thus the only correct level to fight against this particular instance of private censorship is indeed the private domain, and that's mainly counter-speech.