SLA Marshall’s dubious research is well known in military history circles, but he did have experience as a combat infantryman in World War I. Dave Grossman, on the other hand, has had no combat experience as near as I can tell. He throws around his rank and his Ranger School experience, but without any combat experience, I find his credibility suspect.
My own experience is that training is essential to making effective combat soldiers, but training is not about overcoming their reluctance to kill, training teaches them how to effectively use their equipment, including weapons; it teaches them how to work together as a combat unit, and it give them confidence that they can do the job. Couple that training with good leadership and soldiers will perform well in combat including killing the enemy.
This is a bunch of psychobabble from some guy who wants everyone to believe that he is a real warrior. He is a trained soldier, but his lack of combat experience is a glaring hole in his resume.
I have always found Dave Grossman’s claims to be dubious. People have been very effectively killing others outside their group for all of human experience.
It is possible for humans to integrate feelings of goodwill toward strangers, but mostly that would be Christian experience or a philosophy that is taught them.
The historical and archeological evidence is that men kill strangers very easily.
I highly recommend War before Civilization: The Myth of the Peaceful Savage
http://www.amazon.com/War-Before-Civilization-Peaceful-Savage/dp/0195119126
Something that gets left out of this is the flinch factor, fear, I read once that in a firefight, the advantage often goes to the side that first gains the upper hand, because it is difficult for men to force themselves to expose their face to the incoming bullets and violence to return aimed fire, and take control of the situation, when that control is already the other side’s.
The advantage in quality troops or elite troops, is that individually they are more able to force themselves to face the enemies dominance and incoming bullets, to assert the return fire necessary to take away that dominance, and to force the switch-over to get the enemy cowering and losing control over the situation.
I can see how in some situations, troops just get overwhelmed at the beginning with the result that many just hunker down, and have a low rate of return fire, (at least effective return fire).