There should be some kind of line drawn when a service is something people are essentially forced to rely on or is so ubiquitous. "Common carrier" phone companies aren't allowed to selectively censor your use of them, and it seems reasonable that something the likes of Facebook should maybe have to be held to a similar standard when it's so ubiquitous and a major part of modern communication. There are also precedents such as malls not being allowed to limit speech on the premises in California, along with some other states having similar enforcement of certain rights on some kinds of private property.