People kill because it’s the right thing to do.
In their book, Virtuous Violence: Hurting and Killing to Create, Sustain, End, and Honor Social Relationships, moral psychologist Tage Rai at Northwestern and psychological anthropologist Alan Fiske at UCLA sketch the extent to which their work shows that violent behavior among human beings is often not a breach of moral codes but an embodiment of them.
In a way, we all know this, by way of the exceptions we permit. Augustine’s theory of the Just War arose because his god demonstrably approved of some wars. When Joshua fought the battle of Jericho, he had divine approval, "thou shalt not kill" be damned. To Augustine’s credit and others in that tradition, the Just War theory represents hard work to resist as much licit violence as possible. To their discredit, it represents their decision to cave in to questionable evidence and put a stamp of approval on slaughter. (Am I hallucinating to remember a small thumbnail woodcut of Augustine in the margin of a Time essay on the debates over the justice of the Vietnam War? If my hallucination is correct, then I remember shuddering at the sight.)
And certainly we have plenty of examples closer to date: Mideast terrorists and anti-abortion assassins are flamboyant examples, but elected statesmen—American no less than from countries we aren’t so fond of—are no less prone to pull the trigger on killing with exact justifications based in the soundest moral arguments. We glance away nervously and mutter about exceptions. What if the exceptions are the rule?
If the work of Rai and Fiske wins assent, it points to something more troubling. The good guys are the bad guys. Teaching your children to do the right thing can get people killed. We have other reasons for thinking the traditional model of how human beings work in ideal conditions (intellectual consideration of options informed by philosophical principles leading to rational action) may be not just flawed but downright wrong. Rai/Fiske suggest that the model is not even sustainable as a working hypothesis, or faute de mieux, but is downright dangerous.