From Valleywag (warning: heavily airbrushed and quite cleavagey model picture after the link): "...that's the thing about being impolite online: it might be needlessly abrasive 95 times out of 100, but those other five times it's awesome, conveying fresh perspective readers would not have seen were it not for the cloak of anonymity. Cohen says we should make anonymity utterly shameful, except in cases where there is a "reasonable fear of retribution," but this sort of etiquette is basically just a way of regulating opinion, and runs counter to the rawness that has historically been one of the Web's great strengths. You could say the same thing about Wikipedia's new mechanisms for institutional control. Anonymous writers might not always absolutely need the secrecy the shroud themselves in, but they have good reason to want it.
Put another way, if we have to choose between prim scolds like Randy Cohen and impolitic ankle-biters like Fake Steve Jobs (anonymous for many months) or NYTPicker, we'll take the latter any day, even if the price is wading through tons of crap."
I don't think people should be required to be nice all the time. I'm all for free speech, and rawness is part of the deal -- sometimes the truth hurts. But I think each individual should have a pretty high mental bar that they have to clear before they are willing to engage in anonymous, ad hominem attacks. I agree that anonymity has its place, but those who engage in it for selfish, hurtful reasons should be ashamed. I think it's non-sensical to say "this sort of etiquette is basically just a way of regulating opinion" -- etiquette doesn't regulate anything. People should be embarrassed if they engage in this kind of thing without a good reason, and to say they shouldn't be embarrassed because they may censor themselves is to miss the point. I think individuals should censor themselves, but they shouldn't be censored. That's how etiquette works.