The shareholders of Facebook are entitled to run their company as they see fit. Because they own it. Like you can paint the walls of your house whatever colour you like, and if visitors don't like it, then that's their problem.
If we think that Facebook has grown too powerful and intrusive into society to be governed by its shareholders, then nationalisation is completely the correct way to go.
Of course, which nation gets to buy Facebook is another concern... given its global reach, is it really appropriate for the US government to own it? Should the UN "globalise" it instead of the US "nationalising" it?
The analogy also doesn’t work because it’s impossible to have 4 billion people in your house.
That isn't entirely true when we are talking about "customer discrimination"...we'd be having a completely different conversation if Facebook came out and said "we're going to ban Filipinos" or "we're banning those who express anti-war sentiments"...it's a lot easier when the people being persecuted are right-wing nationalists, anti-Israel, or conspiracy nuts...
In addition, the US federal government only exists to protect the innumerable rights of US citizens. Some of these rights are enumerated in the constitution. It is therefore well within the scope of the federal government to protect citizens against bully companies like Facebook who are infringing on these rights.