A journal of a US Marine about Guadalcanal (Pacific) in WW2 is somewhere on the Internet. Stay with me here...I found the Guadalcanal site with his and many other soldiers' experiences, but only by chance. This one guy said that most Japanese soldiers would pretend to surrender and then either shoot at their would-be captors or try to throw a grenade etc. Therefore, this Marine stated that his fellow soldiers shot most of the Japanese who appeared to surrender, at least during one series of battles on Guadalcanal. Can we blame them? Read about the conditions there, at Tarawa and Iwo Jima etc-never mind in Burma. Someone stated that after men have killed a few enemy combatants, it gets much easier, and it can be difficult to control the urge. If I knew that it would almost certainly save some friends' or allies lives, it would get easier for me too.
This may have no real connection to the various situations in Iraq. But can certain similar situations (have they not happened in Iraq or Afghanistan?) create what to civilians, appear to be cold-blooded killing, but are based on numerous last-minute tricks by an enemy, who nowadays wears no uniform and can be everywhere? Maybe these tricks don't happen in Iraq? There is no chance that non-combat people can understand what it is like to be in those situations, anymore than I can understand what it was like to have been a soldier in Julius Caesar's legions, or on stage as lead guitar with the Clash.
As for killing civilians during WW2, we know that it was quite common to carpet-bomb or fire-bomb entire cities (a new article about Dresden's rebuilt Frauenkirche Cathedral, and the English vicars or bishops who visited as an embassy of peace, just came out in our paper, along with debates about the three bombing missions), in order to blast whatever targets. I don't know how many tens of thousands of civilians died on various sides, just in WW2 (!), even though it was not intentional in most cases. My experiences are non-combat. Many years ago, I flew some transport ANG C-130s and then Navy Reserve DC-9s, and have been civilian for the entire time. Had I been born with the WW2 generation, I might have been a B-26, -17 or B-24 crewmember, or even on a Stirling or Lancaster, and tried to do my job. I certainly do not envy those whose mission it is to fight in Iraq or Afghanistan: often a life-or-death mission. I watched an episode during a layover about the medical tents in Iraq, and the young faces of our injured troops. Many are only two years older than my school-age son. This made it difficult for me to watch those blood-covered young men. Were my son there, I would want him to do whatever he thought necessary to survive, against an enemy who, especially with Al Qaeda, merely worships "the cult of death", to quote an excellent editorialist with the New York Times (Friedmann). Many seem to fight with a ferocity borne of religious hatred-by perverting religious beliefs. Did they not also murder a British lady? It would be wonderful if we could tell the virgin Iraqi "government" to have their own police and military soon run their country, then we steadily bring all of our troops home, but my opinion is worth very little.