U.S. paratroopers of the 173rd Airborne Brigade hunt for communist guerrillas in the swampy jungles of zone D, some 40 miles northeast of Saigon, Vietnam, on June 1, 1965. (Horst Faas/AP)

Courtland Milloy, in his Oct. 4 Metro column, "A tragic reminder of capacity for killing," quoted a statement by a participant in the Ken Burns and Lynn Novick documentary on the Vietnam War. Karl Marlantes, who served in the Marine Corps in that war, said, "We're a very aggressive species. It is in us. People talk a lot about how well the military turns kids into killing machines. I always argue that it's just finishing school."

Marlantes's statement is contradicted by the evidence presented in a book published in 1996, "On Killing: The Psychological Cost of Learning to Kill in War and Society." The author, Dave Grossman, was at the time a lieutenant colonel in the Army, a psychologist and a former Army Ranger and paratrooper.

Grossman was committed to helping the U.S. military become more effective in fighting wars. He revealed that the Army has to train its members to kill because most people do not want to kill other human beings. He cited a study conducted by the Army after World War II that discovered that in combat only 15 to 20 percent of soldiers fired their weapons and an even smaller percentage fired to kill. The Army then changed its combat training to desensitize soldiers to the humanity of the enemy. The new training was effective, and as a result, 55 percent of the infantrymen in the Korean War fired their weapons, and 90 to 95 percent fired them in Vietnam.

Marlantes's statement may reflect this training. But I think that most of us do not want to kill our sisters and brothers, even if our nation has designated them as enemies. We must be trained to do it.