Earlier quoted context omitted.
Well, limit your ability to speak in private then? That only makes it even more of a constitutional headache!? Freedom of speech is not something that is limited to the public space, but rather public space is where there is most limitation to what you you can say, simply because of the greater potential impact, private speech is way more protected (including things like privacy of mail and telecommunication). I mean…
Because limitations imposed on a medium such as Facebook doesn't limit my ability to speak in private. That's how I see it. It could be argued that Facebook should be infrastructure.
That's not how the law in general and constitutions in particular work!?
Constitutions don't generally say something like "citizens may speak freely". Rather, they say "the state may not limit citizens in speaking freely". And that is intentional. The constitution does not grant rights to citizens, it limits the rights of the state. It's not that the state has to somehow allow people to speak freely somewhere somehow. The whole point is that the state may just not interfere with people speaking freely. Never, nowhere, and under no circumstances. That is, except for exceptions specified in the constitution or where the constitution allows for exceptions to be created in normal law.
And apart from the fact that that just is how constitutions work: It's absolutely essential that they do work that way. A freedom the exercise of which is subject to arbitrary limitations is just not a freedom. Freedom means that you can do what you want to do, not what someone else wants you to do. Now, that does not mean that you cannot do what someone else wants you to do. But it's only a freedom if it's your choice.
In the case of freedom of speech, that means it's your choice where and when to speak. Now, as I said, constitutions only bind the state, so facebook doesn't have to allow you to speak on their platform. But constititutions that contain freedom of speech make it illegal for the state to interfere with where and when people choose to speak, and that includes indirect interference where the state pressures Facebook to not allow someone to speak.
Just as freedom of movement doesn't mean the state has to allow you to move somewhere, freedom of speech doesn't mean the state has to allow you to speak somewhere. Freedom of movement means the state may not interfere with where or when you choose to move, and freedom of speech means the state may not interfere with where, when, or what you choose to say.