Killing is a chain.
Fantasy seems to isolate the act to two belligerents, the slayer and the slain, at least as far as the consequences go. But the truth is that, in law-enforcement, counterinsurgency, and war, the ultimate act is the result of the efforts of dozens if not hundreds of people. Each is a participant. Each owns the experience. Each is changed by it. Permanently.
Those changes are rarely positive.
I thought about the treatment of killing a lot while I was writing The Desert Wall and The Red Fortress, and how casual it can seem for the character who is doing the killing. I didn’t think that seemed very realistic, but rather a product of casual killing on TV, in the movies and in video games.
More things to read (besides Mike Cole’s post in its entirety): What It Is Like To Go To War by Karl Marlantes and On Killing: The Psychological Cost of Learning to Kill in War and Society by David Grossman