War and Psychopathy
In studies carried out after the Second World War by a military historian, General S. L. A. Marshall. He interviewed thousands of American infantrymen and concluded that only 15 to 20 percent of them had shot to kill. The others had aimed high or hadn't even pulled the trigger, and instead had dedicated themselves to doing what they could at the time.
On the other hand, it was discovered that 98 percent of the soldiers who did shoot to kill had been deeply traumatized by their actions. The remaining two percent were diagnosed as "aggressive psychopathic personalities" who essentially didn't care about killing people under any circumstances, whether at home or abroad.
The conclusion - in the words of Lieutenant Colonel Dave Grossman of the Killology Research Group - was that "there is something about continuous, inescapable combat that drives 98 percent of men mad; "The other two percent were already crazy before."
