Turns out this guy had suffered a traumatic brain injury in Iraq, but was cleared for duty again.
War when conducted by civilized countries is not about killing or even destroying, it's about trying to end the ability of the guy who is trying to destroy you to do so, which unfortunately often involves killing or destroying a few, but even then, they try to limit it to killing solely the people who are killers and the enemy's infrastructure. That is why civilized countries (liberal democracies) virtually never go to war with one another. It's usually with oppressive, militaristic countries or because of oppressive, militaristic countries. For example, Adolf Hitler's Germany in WWII, Imperial Japan in WWII, the Korean War was due to the communists trying to take over all of Korea and the North Koreans being backed by the Chinese and the Soviet Union, Vietnam again due to communists, etc...and in doing so, Western militaries go out of their way not to kill innocents. People being murdered, brutalized, and killed senselessly is an inherent part of humanity, but it is not an inherent part of modern warfare by civilized nations, who go out of their way not to do such things. If a Western army comes into a nation, it isn't going to murder, rape, pillage, or brutalize anybody. People would only be killed if absolutely necessary, which is usually those who started the war in the first place by murdering others.
Keep in mind as well that the strategy being applied in Afghanistan is to make friends with the peoples there to turn them against the terrorists in the region, who are very brutal to them. This strategy worked in Iraq, where Al-Qaeda was so brutal to the Iraqis that it turned even peoples who might have been inclined to ally with it against them. In conventional wars, blatant murder doesn't make sense from a logistical standpoint.