From this principle, many libertarians believe, the rest of libertarianism can be deduced as a matter of mere logic. What is the proper libertarian stance on minimum wage laws? Aggression, and therefore wrong. What about anti‐​discrimination laws? Aggression, and therefore wrong. Public schools? Same answer. Public roads? Same answer. The libertarian armed with the NAP has little need for the close study of history, sociology, or empirical economics. With a little logic and a lot of faith in this basic axiom of morality, virtually any political problem can be neatly solved from the armchair.

On its face, the NAP’s prohibition of aggression falls nicely in line with common sense. After all, who doesn’t think it’s wrong to steal someone else’s property, to club some innocent person over the head, or to force others to labor for one’s own private benefit? And if it’s wrong for us to do these things as individuals, why would it be any less wrong for us to do it as a group – as a club, a gang, or…a state?

But the NAP’s plausibility is superficial. It is, of course, common sense to think that aggression is a bad thing. But it is far from common sense to think that its badness is absolute, such that the wrongness of aggression always trumps any other possible consideration of justice or political morality. There is a vast difference between a strong but defeasible presumption against the justice of aggression, and an absolute, universal prohibition. As Bryan Caplan has said, if you can’t think of counterexamples to the latter, you’re not trying hard enough. But I’m here to help.