Hollywood is great at making war seem so simple and strait forward. It makes the watcher believe that people kill each other because they are told, because it is kill or be killed, the enemy is hated or whatever. Hollywood tries to make us believe that all soldiers fire at each other, desperately attempting to hit and kill each other. While there is some truth in the matter, it is mostly wrong.
An excellent book to read on this subject is "On Killing : The Psychological Cost of Learning to Kill in War and Society" by Dave Grossman. I highly recommend you read this book as it goes into great detail on the subject, much more than can be covered here.
When most people talk about killing, they are like virgins talking about sex. You can talk about it all day, you can fully understand the mechanics involved but when the time comes there is so much more involved than the person thought.
When bullets start flying emotions start running high and that can have a powerful effect on
how a person sees things. Five hundred combatants can see five hundred different things. In
war every fighter see's things differently. The movies like to make people think that the world is
black and white, not different shades of gray.
A look at history might help illustrate what I am talking about. In World War Two, it is a fact that only 15-20 percent of the soldiers fired at the enemy. That is one in five soldiers actually shooting at a Nazi when he sees one. While this rate may have increased in desperate situations, in most combat situations soldiers were reluctant to kill each other. The Civil War was not dramatically different or any previous wars.
In Korea, the rate of soldiers unwilling to fire on the enemy decreased and fifty five percent of the soldiers fired at the enemy. In Vietnam, this rate increased to about ninety five percent but this doesn't mean they were trying to hit the target. In fact it usually took around fifty-two thousand bullets to score one kill in regular infantry units! It may be interesting to not that when Special Forces kills are recorded and monitored this often includes kills scored by calling in artillery or close air support. In this way SF type units could score very high kill ratios like fifty to a hundred for every SF trooper killed. This is not to say these elite troops didn't score a large number of bullet type kills. It is interesting to note that most kills in war are from artillery or other mass destruction type weapons.
If one studies history and is able to cut through the hype, one will find that man is often unwilling to kill his fellow man and the fighter finds it very traumatic when he has to do so. On the battlefield the stress of being killed and injured is not always the main fear.