A username isn't the same as anonymity. You can look through my comment history (and as it happens get a pretty good idea of what I do and where I come from). And my username relates pretty closely to my real name. That isn't much protection of my identity.
Total anonymity (no username, no identity) opens the door for anyone to say anything. In some cases that's good. But IME, it is a benefit that ia mainly used by the dregs .