Earlier quoted context omitted.
If FB are blocking things that they deem bad, then they are clearly setting themselves up as arbiters of morality, even if they say they aren't.
Facebook has opinions about the type of content they'd prefer not to facilitate on the Facebook platform, that doesn't make them "arbiters of morality", it just makes them curators of their product identity.
But that's in fact a moral judgement! It's saying "some people think $X is bad, and we agree with them (or at least choose to pretend to so as not to soil our image)".