Historically - Only one in every ten soldiers on a field actually AIM at the enemy - the rest fire over the heads, or redirect their fire elsewhere. There has always been around 2% that kill all the time - about the sociopath rate.
Killing another human being takes a TERRIBLE toll on any sane person.
On Thursday - reading some current medical research literature at UT Southwest - it is now being reported that the percentage of U.S. Soldiers that have killed in combat is up from 33% a couple of years ago to a staggering and mind blowing rate of 48%.
Do we actually understand the horrible toll this is taking on our youngest and bravest ? We are destroying our fine men and women that are serving this country. I have not a single doubt that this is being done with absolute malevolent intent.
Grossman's conclusions discussed quite intelligently here: http://www.journal.dnd.ca/vo9/no2/16-engen-eng.asp

Finally, brethren, whatsoever things are true, whatsoever things are honest, whatsoever things are just, whatsoever things are pure, whatsoever things are lovely, whatsoever things are of good ...