Not only has the GP indicated one case (JWs) but there are shopping mall cases and many others where a “public forum” doctrine has extended 1A scrutiny to private property.
(That said I think the analog here for the public forum is somewhere well down the OSI stack. In Layer 7 I am pretty firmly a believer that the private actor discriminates how she pleases.)
Really? Because most of YouTube and Facebook very much strikes me as public space. That's how the population thinks of it. That's how society uses it.
You would be protecting a wholly imaginary free speech interest while trespassing on a real one.
Does anyone really think that YouTube not getting to censor people is hampering YouTube's ability to express their political expression? No one in 2018 mistakes a random YouTuber's opinion for YouTube's. Only people interested in silencing others hold to such an opinion. Such an opinion only makes sense, if you directly equate censorship to "expression."
YouTube does have an editorial stake to the product that they can present to their advertiser customers. However, YouTube has stepped way beyond that line! The same goes for Facebook.
Nobodies rights will be violated by this.
The first amendment says that the government cannot restrict free speech it has nothing whatsoever to do with a private entity tolerating "free speech" on their property.
The totality of the public space being private property in the aforementioned scenario sounds like a unique situation and a poor position to reason from.
In general not only do you not have a free speech interest in communicating on someone else's property the government forcing facebook to carry your message would actually be compelling them to communicate their approval of your message.
You would be protecting a wholly imaginary free speech interest while trespassing on a real one.