[Synthetase]

Historically, soldiers have generally been reluctant to use their weapons. During WWII, around 20% of soldiers actually fired their weapons in combat. Even fewer shot to kill often aiming over the heads of the enemy. This is a form of posturing both to the enemy and their comrades. Through extensive use of conditioning, that rate and lethality of fire was raised during Vietnam and subsequent wars.

Even among tribal societies, warfare is highly ritualized in a manner that does not optimize for maximum lethality. Richard Gabriel, in studies on tribal societies in New Guinea have noted that hunts occurred with accurate feathered. Tellingly, tribal warfare employed featherless arrows. Similarly "counting coup" among American Indians involves touching rather than killing the enemy.

Cold blooded killers have their uses for society, especially in warfare. An excellent book on this subject is On Killing.

[philwelch]

Cold blooded killers aren't synonymous with psychopaths. It turns out that many of the Nazis weren't psychopaths, but rather psychologically unremarkable people whose institutions and culture allowed them to collectively perform acts of evil over and above what any of them could have done individually. This is called the "banality of evil", and it became widely understood after the Milgram experiment and the Eichmann trial.

Groups of people have always been more ruthless than individuals. Psychopaths are remarkable not in their ruthlessness but in their ability to achieve it all by themselves.

[declan]

This is a point that the late Jungian psychologist James Hillman raised (and I encountered for the first time) in his book a decade ago titled "A Terrible Love of War." http://www.amazon.com/Terrible-Love-War-James-Hillman/dp/014...

It's different than the normal HN fare, but worth a read. We may be a society of killer apes, but we're not as eager to kill in warfare as you might think. Especially when the other guy was compelled at gunpoint by his government to join the military (that is, drafted) just like you were.

[berntb]

The point was, with the attitude to strangers in clan warfare (not modern post-clan societies), psychopaths have nothing to add regarding ruthlessness. See old Scandinavia.

For stylized cattle raids (e.g. historical Ireland, before the vikings) among old neighbors, there will of course be agreed levels below extermination (or the neighbours will be gone long before western contact).

[maxerickson]

It can just be an unfortunate synthesis of advantageous traits.

Detachment is pretty clearly a (potentially) useful trait for a leader. Same thing for stuff like charisma.