Maximum range.
Artillery crews, bomber crews, naval gunners, and missile crews — at sea and on the ground — are all protected by the same powerful combination of group absolution, mechanical distance, and, most pertinent to our current discussion, physical distance.
...gunners fire at grid references they cannot see; submarine crews fire torpedoes at "ships" (and not, somehow, at the people in the ships); pilots launch their missiles at "targets."
In years of research and reading on the subject of killing in combat I have not found one single instance of individuals who have refused to kill the enemy under these circumstances, nor have I found a single instance of psychiatric trauma associated with this type of killing. Even in the case of the individuals who dropped the atomic bombs on Hiroshima and Nagasaki, contrary to popular myth, there are no indications of psychological problems. Historical accounts indicate that the pilot of the aircraft that made the weather reconnaissance for the Enola Gay had a series of disciplinary and criminal problems before the bombing, and it was his continued problems after leaving the service that formed the sole basis of the popular myth of suicide and mental problems among these crews.

Long range.
...is...the range at which the average soldier may be able to see the enemy, but is unable to kill him without some form of special weaponry — sniper weapons, anti-armor missiles, or tank fire.
Here we begin to see some disturbance at the act of killing as an WWI Australian sniper remembered: "a queer thrill shot through me, it was a different feeling to that which I had when I shot my first kangaroo when I was a boy. For an instant I felt sick and faint; but the feeling soon passed."
These people have the same buffers as maximum range killers have. snipers doctrinally operate as teams, and like maximum-range killers they are protected by the same potent combination of group absolution, mechanical distance (the rifle scope), and physical distance.
They also can rationalize as they can choose targets and many of them opts with killing the brass which is a also a very productive way to destroy the enemy fighting power. If there's no officer to call the shots the grunts won't know what to do.
Nice statistics: From January 7 to July 24, 1969, U.S. Army snipers in Vietnam accounted for 1,245 confirmed kills, with an average of 1.39 bullets expended per kill.
Despite this only a small number of snipers are real killing machines. Only a few of them who produces such long lists of corpses.
Fighter pilots are long range firers too, they have two layers of machinery between them and their victims (other pilots) what they lack is the team's support. ...only 1 percent of U.S. fighter pilots accounted for nearly 40 percent of all enemy pilots shot down in World War II; the majority apparently did not shoot anyone down or even try to.