Not the best source, but this is common knowledge in many circles:

"In a squad of 10 men, on average fewer than three ever fired their weapons in combat. Day in, day out — it did not matter how long they had been soldiers, how many months of combat they had seen, or even that the enemy was about to overrun their position. This was what the highly regarded Brigadier General Samuel Lyman Atwood Marshall, better known as S.L.A. Marshall, or ‘Slam,’ concluded in a series of military journal articles and in his book, Men Against Fire, about America’s World War II soldiers. "

http://www.historynet.com/men-against-fire-how-many-soldiers...

And: "This was a problem for the US military and its allies during World War II. New training implements were developed and hit rates improved. The changes were small, but effective."

https://en.wikipedia.org/wiki/Killology

(playing the devil's advocate) You did note the issues with your sources, but another issue here is both seem to reference western societies, which are guilt[0] societies while asian cultures in general are shame[1] based. This can imply differences in individual morals in people in these cultures.

[0] https://en.wikipedia.org/wiki/Guilt_society

[1] https://en.wikipedia.org/wiki/Shame_society

How does the intentional murder of innocents not cause public/societal shame though? The article mentions such murders have caused outrage, so while some may get off lightly in court it would surely bring shame to the person who committed the act.

S.L.A. Marshall made up his figures from whole cloth. There's no evidence he ever did the research he claimed to have done upon which those figures are based.

Below quote from http://www.warchronicle.com/us/combat_historians_wwii/marsha.... Emphasis not in original This calculation assumes, however, that of all the questions Marshall might ask the soldiers of a rifle company during his interviews, he would unfailingly want to know who had fired his weapon and who had not. Such a question, posed interview after interview, would have signalled that Marshall was on a particular line of inquiry, and that regardless of the other information Marshall might discover, he was devoted to investigating this facet of combat performance. John Westover, usually in attendance during Marshall's sessions with the troops, does not recall Marshall's ever asking this question. Nor does Westover recall Marshall ever talking about ratios of weapons usage in their many private conversations. Marshall's own personal correspondence leaves no hint that he was ever collecting statistics. His surviving field notebooks show no signs of statistical compilations that would have been necessary to deduce a ratio as precise as Marshall reported later in Men Against Fire. The "systematic collection of data" that made Marshall's ratio of fire so authoritative appears to have been an invention.

My comment was more about your use of the word "instinct" than the fact that soldiers normally dislike killing. It would not be surprising that some countries have different reactions to killing if this was indeed a moral construct and not an "instinct."

Same thing with the Wikipedia article you link that uses the word "instinct" without justifying it (do we see that in ALL cultures, in babies?)

Interesting. I would suspect that a great amount of the resistance to moving to autonomous warfare (not drone warfare, but weaponry where no human pulls trigger) is by these same soldiers; not so much a matter of being put out of a job, as no longer being able to be the "conscientious objector on the firing line."

>during World War II

What about the previous quarter million years of modern humans killing other humans?

In response to below, many large animals have instincts about not killing their own kind. It is either too physically dangerous (a similarly-sized opponent) or in the case of social animals too socially costly, depriving the group of a member that represents significant investment. Wolves and lions will kill each other, but never casually.