People throughout history have killed, seemingly casually. It's human nature. I would contend that modern society has instilled these feelings of guilt associated with murder specifically against the natural tendency of man.
That's just one example and it isn't exclusive to primates.
On Killing: The Psychological Cost of Learning to Kill in War and Society, Dave Grossman
Quote From Wikipedia
The book is based on SLA Marshall's studies from World War II, which proposed that contrary to popular perception,[1] the majority of soldiers in war do not ever fire their weapons and that this is due to an innate resistance to killing. Based on Marshall's studies the military instituted training measures to break down this resistance and successfully raised soldiers' firing rates to over ninety percent during the war in Vietnam.[2]
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.
Like I said, modern society has instilled feelings of guilt and negative consequences with our comparatively well-developed ethical and justice systems, generally leading to situations where the risk of getting caught murdering someone outweighs the benefits of killing them (go to jail, hell, etc). But flip the risk analysis (eg, what this article is about), et voilà, no problem.
Did I restrict my statement in some way when I said "vast majority"?
I know citing Wikipedia is lazy, but it mentions high murder rates of 35 in 100,000 during medieval times. I know there are other forms of homicide, but I haven't spent the time to find stats. Assuming on average one murderer per victim, %0.00035 is vansishingly small.
Some of the battles are agreed upon ahead of time. Killing in battle is not usually considered murder under law, but even so, the vast majority of people do not murder.
The armed militia was also high on drugs when they confronted the motorists, so their very minds (nature) were changed during the encounter.
Our morals aren't nearly as absolute as we like to think. 20% of the entire population of Rwanda were hacked to death with farm implements by ordinary people. 25% of the Cambodian population were butchered, starved or worked to death by a poorly-organised militia.
Any of us have the capacity to kill if we have a sufficiently compelling justification. Ask any mother if she would kill to save her children. The difference between murder and self defence is mere context - the Nazis believed that they were defending themselves from a Jewish conspiracy, the Interahamwe believed they were liberating themselves from Tutsi oppression.
Consider the fact that the rate of domestic homicide in the US is drastically higher in households that own a gun. A great number of Americans have killed their partner simply because the means to do so easily was readily available. Evil or insanity is not a prerequisite for murder, only means, motive and opportunity.
In the study, he didn't ask his subjects to kill. And they didn't actually murder anyone.
> Rwanda ... Cambodia ... Nazis ... Interahamwe
People killing on behalf of the State is a whole other matter than what the article is talking about vis-à-vis pedestrian fatalities. The State has been the largest single driver of misery, destruction, and death in human history, and I don't disagree that mass murder has happened and is evil. But drivers ensuring the death of a struck passenger stands in stark contrast to the kill-or-be-killed nature of State violence. On this point, I would agree with your assertion about "compelling justification," which in the case of the State is the threat of violence against the killer for not doing the bidding of the State.
But even in the face of multiple genocides and huge wars, including nuclear bomb blasts, the fact remains that the vast majority of humans have never and will never kill another human.
> A great number of Americans ...
See a sibling response for murder rates and compare to my assertion that a vast majority of people don't do it.
And self-defense is not murder by the legal definition, which include premeditation.
[0]: http://www.historynet.com/men-against-fire-how-many-soldiers...
I am an enormous believer in good manners [1].
[1] Which I am much better at in meatspace. Damn you, anonymous internet.
Putting aside the statement's low plausibility of truth, it is certainly the worst thing I've read in quite some time.