And that argument would be correct. Common-carrier rules are a product of law and regulation over the telecom industry, not a Constitutional right. In an unregulated, un-subsidized, purely private telecommunications market, you would have no right to do anything the provider doesn't want you to.

Because there is such a high barrier to entry for basic telecoms infrastructure, this would be extremely problematic for society, and the infrastructure is regulated to prevent the companies from interfering with speech just because they don't like its content.

Facebook is not infrastructure. The infrastructure used to communicate with it can also be used to freely communicate with any other person or service, with a very low barrier to entry. Witness now, you and I and many others are communicating on this very site without any involvement of Facebook whatsoever. Many people use Twitter, Google+, Tumblr, good ol' email, SMS, and various IM services to communicate entirely separate from Facebook. I don't even have a Facebook account, nor do most of the people I have regular in-person contact with -- it holds no appeal to us.

I can setup any number of services and applications in minutes at minimal cost on servers likewise entirely distinct from Facebook that would facilitate a wide variety of communications.

Facebook could shut down tomorrow and the societal disruption would be fleeting and mostly non-fiscal. The hive mind would quickly anoint a successor or two, and life would go on.

If, somehow, all the major telecom companies and their infrastructure disappeared tomorrow, severe economic disruption would occur, and it would take years, probably decades, to restore full service, much less recover from the economic collapse.

Thus is the distinction between a popular social networking service run on top of a telecommunications network, and the telecommunications network itself, and thus the disparity in law and rights.