A little over three years ago, I published an essay entitled, “Six Reasons Libertarians Should Reject the Non-Aggression Principle.” That essay kicked off a spirited debate, with notable responses from George Smith, David Gordon, and Julian Sanchez, among others.
Since then, I haven’t written much about the issue for the blogosphere. But I have been thinking about it. And the result of that thinking has now been published in a new essay, “The Libertarian Nonaggression Principle,” out today in the newest issue of the journal Social Philosophy and Policy. 
The short version of my thesis is: I don’t actually think we should “reject” the non-aggression principle, but I don’t think we can really base a libertarian theory off it either.
The longer version’s in the abstract:
Libertarianism is a controversial political theory. But it is often presented as a resting upon a simple, indeed commonsense, moral principle. The libertarian “Nonaggression Principle” (NAP) prohibits aggression against the persons or property of others, and it is on this basis that the libertarian opposition to redistributive taxation, legal paternalism, and perhaps even the state itself is thought to rest. This essay critically examines the NAP and the extent to which it can provide support for libertarian political theory. It identifies two problems with existing libertarian appeals to the NAP. First, insofar as libertarians employ a moralized understanding of aggression, their principle is really about the protection of property rights rather than the prohibition of aggression. Second, the absolutist prohibition on aggression, which libertarians typically endorse and which is necessary to generate strongly libertarian conclusions, is grossly implausible. The essay concludes by setting forth a version of the NAP that does not suffer from these problems. It argues that this more moderate and defensible version of the NAP still has important libertarian implications, but that a full defense of libertarianism cannot rely upon appeals to nonaggression alone.
Read the whole thing here.
 That issue contains some other fantastic essays as well, including one by our own Jason Brennan entitled, “When May We Kill Government Agents? A Defense of Moral Parity,” and one by Eric Mack on “Elbow Room for Self-Defense.” Both of those essays, unfortunately, are gated. But maybe if you bug Jason or Eric they’ll give you a free copy.