Free speech rights are limited to government intervention, for good reason. The only question from a free-market perspective is whether or not Facebook has provided the tools to self-censor the content you get in your social network, much like HN where you can downvote/flag content that is inappropriate or of questionable quality [1]. That would downplay the monopolistic side effects of not having a competitor to go to if you're not happy with Facebook's strict censoring rules.

[1] I should note Facebook already does provide lots of ways to filter people from your feed without unfriending them if you don't like what they post.