Yeah, the most important benefit of Facebook is that you can say things "privately". But even then, it's a lot harder to portray someone as an evil villain cartoon when there's context.

Even if most people don't read more than a sentence or two, it's possible to look like a real human being, whereas on Twitter you get your 140 characters, and that's that. By the nature of the network, nobody cares or sees the ten tweets that come before/after the offending one.