The libertarian ethic does not say that aggression is never justified, but that it is always criminal. Note that these are very different things. One might feel justified in committing a prima facie criminal act in the belief that he will be subsequently pardoned or even thanked by his victim (think, of, e.g., forcibly preventing a temporarily depressed would-be suicide from carrying through on his plans). And note that this is something very different from allowing for the existence of a monopolistic apparatus of aggression that removes itself from the ambit of universally applicable morality by claiming that its acts of aggression are not criminal-though-pardonable, but possibly non-criminal.

The libertarian ethic says: aggression may occasionally be justified, but it always – though not necessarily permanently – makes the aggressor a criminal. The statist (pseudo)ethic says: aggression may be non-criminal, provided that it is committed by the right kind of aggressor. This is neither a trifle nor a concession, but the essence of the difference between sophisticated morality and sophistical immorality.