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.
Proposition (b) is plainly false. States always tax their citizens, which is a form of aggression. They always outlaw competing defense agencies, which also amounts to aggression. (Not to mention the countless victimless crime laws that they inevitably, and without a single exception in history, enforce on the populace. Why minarchists think minarchy is even possible boggles the mind.)
As for (a), well, socialists and criminals also feel aggression is justified. This does not make it so. Criminals, socialists, and anti-anarchists have yet to show how aggression — the initiation of force against innocent victims — is justified. No surprise; it is not possible to show this. But criminals don’t feel compelled to justify aggression; why should advocates of the state feel compelled to do so?
Conservative and minarchist-libertarian criticism of anarchy on the grounds that it won’t "work" or is not "practical" is just confused. Anarchists don’t (necessarily) predict anarchy will be achieved — I for one don’t think it will. But that does not mean states are justified.
Consider an analogy. Conservatives and libertarians all agree that private crime (murder, robbery, rape) is unjustified, and "should" not occur. Yet no matter how good most men become, there will always be at least some small element who will resort to crime. Crime will always be with us. Yet we still condemn crime and work to reduce it.
Is it logically possible that there could be no crime? Sure. Everyone could voluntarily choose to respect others’ rights. Then there would be no crime. It’s easy to imagine. But given our experience with human nature and interaction, it is safe to say that there will always be crime. Nevertheless, we still proclaim crime to be evil and unjustified, in the face of the inevitability of its recurrence. So to my claim that crime is immoral, it would just be stupid and/or insincere to reply, "but that’s an impractical view" or "but that won’t work," "since there will always be crime." The fact that there will always be crime — that not everyone will voluntarily respect others’ rights — does not mean that it’s "impractical" to oppose it; nor does it mean that crime is justified. It does not mean there is some "flaw" in the proposition that crime is wrong.
Likewise, to my claim that the state and its aggression is unjustified, it is disingenuous and/or confused to reply, "anarchy won’t work" or is "impractical" or "unlikely to ever occur."1 The view that the state is unjustified is a normative or ethical position. The fact that not enough people are willing to respect their neighbors’ rights to allow anarchy to emerge, i.e., the fact that enough people (erroneously) support the legitimacy of the state to permit it to exist, does not mean that the state, and its aggression, are justified.2
Other utilitarian replies like "but we need a state" do not contradict the claim that states employ aggression and that aggression is unjustified. It simply means that the state-advocate does not mind the initiation of force against innocent victims — i.e., he shares the criminal/socialist mentality. The private criminal thinks his own need is all that matters; he is willing to commit violence to satisfy his needs; to hell with what is right and wrong. The advocate of the state thinks that his opinion that "we" "need" things justifies committing or condoning violence against innocent individuals. It is as plain as that. Whatever this argument is, it is not libertarian. It is not opposed to aggression. It is in favor of something else — making sure certain public "needs" are met, despite the cost — but not peace and cooperation. The criminal, gangster, socialist, welfare-statist, and even minarchist all share this: they are willing to condone naked aggression, for some reason. The details vary, but the result is the same — innocent lives are trampled by physical assault. Some have the stomach for this; others are more civilized — libertarian, one might say — and prefer peace over violent struggle.
As there are criminals and socialists among us, it is no surprise that there is a degree of criminal-mindedness in most people. After all, the state rests upon the tacit consent of the masses, who have erroneously accepted the notion that states are legitimate. But none of that means the criminal enterprises condoned by the masses are justified.
It’s time for libertarians to take a stand. Are you for aggression, or against it?