Many libertarians believe that the whole of their political philosophy can be summed up in a single, simple principle. This principle—the “non-aggression principle” or “non-aggression axiom” (hereafter “NAP”)—holds that aggression against the person or property of others is always wrong, where aggression is defined narrowly in terms of the use or threat of physical violence.

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.

In the remainder of this essay, I want to present six reasons why libertarians should reject the NAP. None of them are original to me. Each is logically independent of the others. Taken together, I think, they make a fairly overwhelming case.

1. Prohibits All Pollution – As I noted in my last post, Rothbard himself recognized that industrial pollution violates the NAP and must therefore be prohibited. But Rothbard did not draw the full implications of his principle. Not just industrial pollution, but personal pollution produced by driving, burning wood in one’s fireplace, smoking, etc., runs afoul of NAP. The NAP implies that all of these activities must be prohibited, no matter how beneficial they may be in other respects, and no matter how essential they are to daily life in the modern industrialized world. And this is deeply implausible.
2. Prohibits Small Harms for Large Benefits – The NAP prohibits all pollution because its prohibition on aggression is absolute. No amount of aggression, no matter how small, is morally permissible. And no amount of offsetting benefits can change this fact. But suppose, to borrow a thought from Hume, that I could prevent the destruction of the whole world by lightly scratching your finger? Or, to take a perhaps more plausible example, suppose that by imposing a very, very small tax on billionaires, I could provide life-saving vaccination for tens of thousands of desperately poor children? Even if we grant that taxation is aggression, and that aggression is generally wrong, is it really so obvious that the relatively minor aggression involved in these examples is wrong, given the tremendous benefit it produces?
3. All-or-Nothing Attitude Toward Risk – The NAP clearly implies that it’s wrong for me to shoot you in the head. But, to borrow an example from David Friedman, what if I merely run the risk of shooting you by putting one bullet in a six-shot revolver, spinning the cylinder, aiming it at your head, and squeezing the trigger? What if it is not one bullet but five? Of course, almost everything we do imposes some risk of harm on innocent persons. We run this risk when we drive on the highway (what if we suffer a heart attack, or become distracted), or when we fly airplanes over populated areas. Most of us think that some of these risks are justifiable, while others are not, and that the difference between them has something to do with the size and likelihood of the risked harm, the importance of the risky activity, and the availability and cost of less risky activities. But considerations like this carry zero weight in the NAP’s absolute prohibition on aggression. That principle seems compatible with only two possible rules: either all risks are permissible (because they are not really aggression until they actually result in a harm), or none are (because they are). And neither of these seems sensible.
4. No Prohibition of Fraud – Libertarians usually say that violence may legitimately be used to prevent either force or fraud. But according to NAP, the only legitimate use of force is to prevent or punish the initiatory use of physical violence by others. And fraud is not physical violence. If I tell you that the painting you want to buy is a genuine Renoir, and it’s not, I have not physically aggressed against you. But if you buy it, find out it’s a fake, and then send the police (or your protective agency) over to my house to get your money back, then you are aggressing against me. So not only does a prohibition on fraud not follow from the NAP, it is not even compatible with it, since the use of force to prohibit fraud itself constitutes the initiation of physical violence.
5. Parasitic on a Theory of Property – Even if the NAP is correct, it cannot serve as a fundamental principle of libertarian ethics, because its meaning and normative force are entirely parasitic on an underlying theory of property. Suppose A is walking across an empty field, when B jumps out of the bushes and clubs A on the head. It certainly looks like B is aggressing against A in this case. But on the libertarian view, whether this is so depends entirely on the relevant property rights – specifically, who owns the field. If it’s B’s field, and A was crossing it without B’s consent, then A was the one who was actually aggressing against B. Thus, “aggression,” on the libertarian view, doesn’t really mean physical violence at all. It means “violation of property rights.” But if this is true, then the NAP’s focus on “aggression” and “violence” is at best superfluous, and at worst misleading. It is the enforcement of property rights, not the prohibition of aggression, that is fundamental to libertarianism.
6. What About the Children??? – It’s one thing to say that aggression against others is wrong. It’s quite another to say that it’s the only thing that’s wrong – or the only wrong that is properly subject to prevention or rectification by force. But taken to its consistent extreme, as Murray Rothbard took it, the NAP implies that there is nothing wrong with allowing your three year-old son to starve to death, so long as you do not forcibly prevent him from obtaining food on his own. Or, at least, it implies that it would be wrong for others to, say, trespass on your property in order to give the child you’re deliberately starving a piece of bread. This, I think, is a fairly devastating reductio of the view that positive duties may never be coercively enforced. That it was Rothbard himself who presented the reductio, without, apparently, realizing the absurdity into which he had walked, rather boggles the mind.

There’s more to be said about each of these, of course. Libertarians haven’t written much about the issue of pollution. But they have been aware of the problem about fraud at least since James Child published his justly famous article in Ethics on the subject in 1994, and both Bryan Caplan and Stephan Kinsella have tried (unsatisfactorily, to my mind) to address it. Similarly, Roderick Long has some characteristically thoughtful and intelligent things to say about the issue of children and positive rights.

Libertarians are ingenious folk. And I have no doubt that, given sufficient time, they can think up a host of ways to tweak, tinker, and contextualize the NAP in a way that makes some progress in dealing with the problems I have raised in this essay. But there comes a point where adding another layer of epicycles to one’s theory seems no longer to be the best way to proceed. There comes a point where what you need is not another refinement to the definition of “aggression” but a radical paradigm shift in which we put aside the idea that non-aggression is the sole, immovable center of the moral universe. Libertarianism needs its own Copernican Revolution.