I think it just takes a reminder of the human on the other side of the machine, as well as the fact that we really wouldn't say the things we post online in real life, face to face. So, the avatar picture of a real person might help.
That’s a great thought but even people won’t believe that. I have very hefty security settings on my Facebook account and despite the fact that my profile picture has always been of me, whenever I’ve gotten involved in conversations with people who I’m not friends with (or aren’t friends of friends), I always get told I’m a fake account. Why the high security settings? Because I’m just as guilty of being untrustworthy of people. *shrugs* It’s a real issue.
In theory, I agree with you. It’s just that people are so generally untrusting of those they encounter. We need to somehow solve that problem first. And that’s gonna be a hard pill for people to swallow.