They could if someone was willing to post pseudonymous for those who want to both be anonymous and have their writing acknowledged and critiqued (which, after all, if you don't want the latter, why are you on LJ at all? They may as well keep the stuff on their computer for a rainy day.)

Such people are my main dilemma. But other than that no, I don't see why they can't be. In fact they often are.