The bothersome effect of pseudynimity is that it gives the rest of us the privilege that AB takes for granted. And that’s the real problem: not that it gives others impunity, but that it creates a situation where impunity ceases to be her special privilege.
This is absolutely correct. The ability to participate in the public discourse is something which previously was available only to a select few, and is now open to everyone. Part of what allows that is the ability of people to not attach their name to everything they write. People who have job and income stability (say, tenured professors) take for granted that they can say just about anything in a public space (such as the internets) without fear of consequence. Many other people, not so much.
The only reason to care about the identity of the person at the other end of the internet is to allow for real world consequences for online activity, consequences that some people are largely shielded from.
There's no reason people should worry that their boss is going to get called if they make some whiny asshole upset on the internet, or that their phone number will get posted, or their children brought into the discussion. But there are assholes on the internet who happily do such things on a regular basis, and it's perfectly sensible to hide a real world identity which has nothing to do with what goes on in the virtual world.
If I'd blogged under the name "Roger Smith" instead of "Atrios" no one would have been the wiser. Knowing what they believed to be a real name would they have been entitled to know all of my personal details? Of course not. And, if not, a name really confers no meaningful information.
Certainly anonymity lets people be bigger assholes than they might otherwise be, but for the most part who cares. It's the internets.