When BBSes started to come about, we were warned repeatedly that censoring content would make us liable for the the contents themselves. If we did not, we could not be held liable. The only place we were told we can limit, is at account sign-up.

What happened to this legal quandary? Facebook is not only a "carrier of posts" but also "arbiter of contents", in essence playing both.

Is Facebook then liable for the contents? I am not referring to DMCA, but libel and related issues.