The most natural way to think about self-defense, for most people, is through the idea of rights. Put in its simplest terms this reflects the intuition that a man who kills in self-defense has a right to act as he does, and that moreover what underlies this is the fact that the aggressor no longer possesses the right not to be killed by him. Through his aggressive actions his right to life has been lost, negated, or somehow annulled. There is no denying that this idea captures a powerful intuition about the way the whole mechanism of defensive rights operates.
On further reflection, however, this simple conception leads to a philosophical quagmire. When applied in a principled way to particular cases it seems to generate deep contradictions and puzzles. Indeed, so difficult has it proved to provide a coherent account of self-defense through the notion of rights that, as we shall see, a number of modern theorists have decried the entire project as hopelessly ill-conceived.
None the less, a coherent rights-based explanation of self-defense can be constructed. I shall argue in this chapter that it provides the best overall approach to completing our understanding of self-defense. In demonstrating this, however, we shall need to push the account a long way from the simple thought about loss of the aggressor's rights articulated here.
As suggested in the last chapter, the primary difficulty for a rights-centred account of self-defense is how to explain what I have called the 'moral asymmetry' between the defender and the aggressor. The problem can be summarized as follows: if the right of self-defense derives from the right to life, and that right is universal, why is it permissible for the defender to kill the aggressor but not the other way around, even though at the moment of engagement each is a threat to the life of the other?