And yet
I did say that in face-to-face, him-or-me context, many people do kill.
But it's not limited to the Civil War. Look at SLAM Marshall's studies of combat in WWII. He did detailed studies of units in combat and esimated that 80-90% of combatants were NOT trigger pullers. They weren't cowards either. Some did other things like treat wounded, run messages or passed ammo to the trigger-pullers, but it was the trigger-pullers who were doing the damage i.e. killing.
It was largely based on his and similar studies that the US Army, USMC changed how they trained people to shoot. Rifle training in WWI and WWII consisted of large, circular targets that would be scored. After WWII, the Army started to take advantage of B.F Skinner's work on psychological conditioning. You know, the experiment where the rat presses the lever, then he gets a good pellet to drop out and therefore the rat learns that he can press on the food lever to be rewarded with a pellet.
During Vietnam, the Army's rifle training was to have soldiers aim at man-shaped targets, which when hit, would drop. Anyone who is familiar with basic these days can relate similar experiences. You see the target pop up, you aim, shoot and the target drops. Your brain is rewarded from the stimulation. This is a lethal version of the lever-food pellet experiment with soldiers as the rat.
Read David Grossman's "On Killing" for a more thorough explanation.
ON KILLING
Of course, it made soldiers in Vietnam more willing to shoot at targets, but it didn't reduce the guilt or regret for killing that these soldiers felt. The Army's dumble whammy, we'll make you a killer, but you'll still feel bad. It's suggested that this is the reason for more PTSD by Viet vets. But that is another topic.