The outrage lies in the abandonment of principle, that even under the duress of war, a respect for core human decency should govern our actions. ANd that when forced away from that respect by the heat of mortal conflict, we should try to return to it as soon as we can breathe easily.
This puts an awful burden of cognitive dissonance on an individual charged with doing the killing. Or the interrogation. And moral fiber is not what our youth are best known for, let alone our military trainees. But we kind of expect it in our over-fed leaders, who don't spend a lot of time facing mortal threat.