I think it's still too early to tell whether facebook is doing anything wrong, but I think they're definitely doing something different and interesting. Not without precedent—cross-site identity systems are nothing new, oauth and disqus, et al—but definitely to a degree and with a scope that hasn't been attempted before.
Apologies if i did not understand your intent in your previous post. That aside, i dislike the notion that the internet is somehow a separate kind of space from the other sorts of social interaction we engage in. There are people who masquerade and are different people IRL just as well as there are online. There are some differences, the sort of transformation and context switch necessary to go between identities/facets is different certainly. But that doesn't change the cognitive/emotional reality.
Besides, who's to say that internet trolls aren't a real part of a lot of people's identities? (I think this is where we agree) Facebook commenting may add a component of IRL social decorum, but imo that has less to do with notions of the self, as just trying not to piss off people who have social currency in your life.
Having a single point of contact w/o the ability to filter or group your interactions scoped to people who you feel comfortable communicating with isn't just lame, it's socially poisonous.
Facebook is doing it wrong.