I think it’s interesting to think those comments can be censored. Certainly they can be controlled when they occur on an organization’s site or one controlled by the organization (i.e. an official Facebook Page), but it has to be clear by now in 2011 that censorship of a social site is like pushing a balloon: the comments will still be posted, they just won’t be as visible *to the organization* – meaning it will be harder to counter them.
If negative comments are made, either the community will address them because they are incorrect, or – perhaps – the community will agree with them because they aren’t. In either case a positive outcome is quite possible, though in the latter it might be more difficult and less comfortable for the organization. What should be of most concern to an organization is either where negative comments aren’t addressed, because there is no community or it doesn’t care – or where there are no comments at all (and likely no community).