The taking of another human life is not the natural order of things, for if it was, there would first of all be far less human life on this planet, and further to the point, the murder of another human being, would not be considered by law to be a heinous crime subject to its appropriate punishment so done. The United States has taken upon itself to be the world's policeman, and hence from there, sticks its nose into all sorts of affairs, of which some of these affairs, apparently necessitate war.
The problem that America has with the present order of things, is unlike wars such as World War I or World War II, which had soldiers on both sides of the war, armed against each other in protracted battles, of one side facing the other; is that today's wars, in so many ways, involved opponents that are not easily discerned, hit and run tactics, and those that make it their point to engage American soldiers not in the open field of battle and thereby far away from civilian centers, but deliberately do so within civilian parameters, and utilize even the guise of civilian garb, as necessary, for the element of surprise and chaos.
That is to say, American soldiers are to a very great extent unsure of who, what, and where the enemy is, and therefore are "on edge" in regards to their point of attack and their tactics to engage the enemy. Further, to the point, when everyone within a given area, could be the enemy, or in consortium with the enemy, or converted by the enemy, then that makes most everyone that American soldiers see, as potential enemy combatants. This thus means, that in engaging the enemy, Americans are going to have a much higher tendency of killing as well as harming people that are wholly innocent of the affair, because when American soldiers are not certain as to the clear identity or intention of the opponent, decisions will be made, of which some of those decisions, will result in lethal action.
Not too surprisingly, for many American soldiers, the taking of another person's life in battle can be rather traumatic emotionally and psychologically, especially when in the aftermath of such an engagement, when the heat of the moment has dissipated, they feel that some of those that have been killed or harmed, were probably not the real enemy at all, but rather were civilians caught in the crossfire of such action.
A soldier with a conscience will be bothered with such, because such a soldier knows that there is a world of difference, between justifying the killing of an enemy soldier, as troubling and as traumatic as that may be, in comparison to the killing of a non-combatant, especially if such a killing was done deliberately via the fog of war. This thus means, that those that have engaged in the most unnatural of brotherly acts, of taking the life of another, especially of someone that is innocent, will thereby frequently suffer the consequences of stress, confusion, doubt, and regret, for the unnatural taking of the life of another human being, is a burden that lays most uneasy upon he who has performed this act.