Justifying Intentional Killing of the Innocent?

Here (thanks to Larry Solum) is the abstract for a new paper, "The Basis of Moral Liability to Defensive Killing" (yes, that's "to", not "for"), by Jeff McMahan, a philosopher at Rutgers:

There may be circumstances in which it is morally justifiable intentionally to kill a person who is morally innocent, threatens no one, rationally wishes not to die, and would otherwise not die soon. The justification in such a case presumably must appeal to the dire consequences that would ensue if the person were not killed. It is the necessity of averting consequences much worse than a single death that would justify the wrong done to the person killed. In other instances of permissible killing, however, the justification appeals to more than considerations of consequences. It may appeal in addition to the claim that the person to be killed has acted in such a way that to kill him would neither be unjust nor wrong him or violate his rights (assuming that killing him would be necessary for and proportionate to a just or legitimate aim, such as self-defense). In these cases, I will say that the person is liable to be killed. Although I borrow the notion of liability from legal theory, and although much of what I say will be informed by the literature on liability both in criminal law and in the law of torts, my concern in this article is with moral rather than legal liability. Liability, as I understand it, encompasses but is not limited to desert. If a person can deserve to be killed, it follows that he is liable to be killed, but he can be liable to be killed without deserving to be killed. My focus here will be on forms of liability that do not involve desert; I will not consider cases of punitive or retributive killing. My focus will instead be primarily on liability to defensive killing, though I will also consider whether there can be liability to killing that preserves life or prevents harm but is not strictly defensive because the person to be killed is not the cause of the threat to be averted. Liability, of course, also extends to forms of harmful treatment other than killing, but for simplicity of exposition I will focus on moral liability to be killed. Much of what I will say, however, can be generalized, mutatis mutandis, to other forms of harming.

I have not read the paper yet, but I would think it would be of great interest to those who have ever wrestled with the necessity, or "choice of evils", defense in criminal law.  Traditionally, the intentional killing of a non-aggressor could not be "justified", even if the killing was reasonably thought "necessary" to avoid a "greater evil."  The Model Penal Code abandoned this approach, and allows a "choice of evils" defense even in cases that would otherwise be homicide.  What strikes me as intriguing about McMahan's paper (and, again -- I have not yet read it) is the focus on the "liability" of the victim "to" killing, and the claim that a "defensive" killing of one who is "liable to be killed" does not violate that person's rights.  I'd welcome (and appreciate!) the reactions to the paper of any experts or moral philosophers out there . . .

Rick