Once in awhile, someone accuses me of "censoring" them for deleting their vitriolic comments from my Wall or my blog. That, I think, is silly - it's my blog, it's not the public sphere.
But there is, I believe, a difference between my blog and Facebook or Google+ on the whole. My Google+ "community" is my Stream. If you're being an asshole, I can block you and prevent you from entering that space.
Community policing involving paid staffers becomes problematic very quickly, however. Sure, there are easy justifications: Child sexual abuse content, death threats, etc. But at the same time, these systems can be abused, and the moderation processes are often opaque.
Case in point: Facebook has banned me from posting a link to the Pirate Bay (to a specific page hosting out-of-copyright articles) because "it's a link that some users believe to contain spammy or abusive content." I can appeal it, which is good, but there's no guarantee that will fix anything. Meanwhile, that perfectly legal (and probably ToS-compliant content) remains impossible for me to link to.
There is also, problematically, the increasing feeling that private spaces are replicating the public sphere. And while, in the public sphere, there is no space for shouting "fire!", there is often space for unpopular opinion that is protected by the First Amendment, but not by Facebook's (or insert your favorite company here) Terms of Service.
There is space for us to moderate content, but there is also space for us to build better, more thoughtful policies.
Note: If you pull a simple "these are private companies, they can do whatever they want", I will ignore you. All of us working on these issues are perfectly aware of that fact, a fact which shouldn't stop us from trying to better these spaces.