Libertarian opponents of anarchy are attacking a straw man. Their arguments are usually utilitarian in nature and amount to "but anarchy won’t work" or "we need the (things provided by the) state." But these attacks are confused at best, if not disingenuous. To be an anarchist does not mean you think anarchy will "work" (whatever that means); nor that you predict it will or "can" be achieved. It is possible to be a pessimistic anarchist, after all. To be an anarchist only means that you believe that aggression is not justified, and that states necessarily employ aggression. And, therefore, that states, and the aggression they necessarily employ, are unjustified. It’s quite simple, really. It’s an ethical view, so no surprise it confuses utilitarians. Accordingly, anyone who is not an anarchist must maintain either: (a) aggression is justified; or (b) states (in particular, minimal states) do not necessarily employ aggression.