In my experience many of the anonymous comments which are mean, snarky, sarcastic, etc, often have a valid point, but the commenter is too lazy to articulate that point in a way that does not come off as trolling.

Perhaps they don't have enough time or enough patience to properly explain themselves, but if that's the case, perhaps leaving no comment is a better option? It's not as satisfying for the venter, but it's a better experience for everyone else.

Making commenter's use a tangible "real" identity makes them think twice about posting lazy rants.