Society has a moral obligation, some argue, to better prepare those sent to war, to provide assistance in combat, and to help in the transition home.
"We have a profound responsibility because we send these people into combat on our behalf, to kill for us," says Shannon French, who teaches ethics at the US Naval Academy in Annapolis, Md.
Postwar tragedy may have been averted, says Mr. Sheehan-Miles, if help had been available to his tank unit. "Within my own tank company, half of the married soldiers were divorced within a year after the Gulf War; one shot another over a girl," he says. "They didn't know how to get help, and the Army essentially did nothing."
Psychological injuries of war can't be tied solely to killing alone - seeing close comrades die and other horrors of war are also factors. But mental-health professionals and chaplains who've worked closely with veterans see killing as a significant contributor, along with other demoralizing elements of combat that soldiers experience or see as "a betrayal of what's right," says Veterans Affairs psychiatrist Jonathan Shay.
The devastating impact of war on soldiers was visible after World Wars I and II and the Korean War as well. But particularly evident today is the ongoing toll of the Vietnam War, whose vets are overrepresented in the homeless and prison populations. One-third are said to suffer from post-traumatic stress disorder (PTSD).
In July, the New England Journal of Medicine reported that 16 percent of veterans of the war in Iraq suffer from depression or PTSD, and that fewer than 40 percent have sought help.
Along with several studies, the efforts of two men are stirring thinking within the US military: Grossman, who wrote "On Killing: the Psychological Costs of Learning to Kill in War and Society," and Dr. Shay, who has worked with vets for 20 years at the VA Outpatient Clinic in Boston. Shay has written two books ("Achilles in Vietnam" and "Odysseus in America") that provide in-depth analyses of how combat can affect individual character and the homecoming to civilian society.