Colonel Russell Williams is one of those double-life people—an able military commander who was also a rapist and murderer. The crimes for which he was sentenced last month were shockingly evil, and that led the Canadian military last week to enact a real-life version of a well-known psychology experiment.

Back in the 1990's the social psychologist Paul Rozin and his colleagues asked people if they would wear Hitler's sweater, and they usually said no, not even if it had been washed, torn or lent to Mother Teresa first. That was an important insight into the mind's rules for reacting to contamination: It showed, first, that those rules don't distinguish between physical and moral impurity and, second, that they're profoundly non-rational. The rules say a sweater's Hitlerness can't be cured by detergent, or a symbolic punishment, nor by spending time on the back of a saint. It's not logical but it's how our minds work (maybe because in Release 1.0, before morality, such a rule prevented our ancestors from getting poisoned).

Such is human nature. But gut instincts and biases can be overcome by appeals to reason. If that weren't true, we wouldn't have armies.

After all, people aren't innately inclined to blind obedience, nor to run toward men with guns. Nor does killing come easily to most of us. (As Dave Grossman has explained, most soldiers in most wars until recently have avoided aiming at the enemy and firing. It takes systematic training, which he describes in his book, to overcome that reluctance to kill.)

This disciplined assault on instinct is the basis of military life. So wars aren't fought because "primitive" emotions overcome reason; they're fought because reason overcomes primitive emotions, and people consciously and conscientiously force themselves to do what doesn't come naturally. Of course, wrote the Air Force General Curtis LeMay, anyone dropping bombs from an airplane will think about the innocents he's killing, "a child lying in bed with a whole ton of masonry toppling on top of him." But a disciplined mind puts those gut feelings aside: "Then you have to turn away from the picture if you intend to retain your sanity. And also if you intend to keep on doing the work your Nation expects of you."

Given that militaries are hyper-rational institutions, I was surprised to see what the Canadian Air Force did with Williams' uniforms and equipment. The logical thing to do with these lifeless materials would be to re-use and recycle them. By contrast, the urge to treat them like Hitler's sweater is unreasoning and instinctive. But that's what the Air Force did with Williams' stuff: Last week, they burned it all.