Andrew J. Bacevich is professor of history and international relations at Boston University.

Riders on Boston subways and trolleys are accustomed to seeing placards that advertise research being conducted at the city’s many teaching hospitals. One that recently caught my eye, announcing an experimental “behavioral treatment,” posed this question to potential subjects: “Are you in the U.S. military or a veteran disturbed by terrible things you have experienced?”

Just below the question, someone had scrawled this riposte in blue ink: “Thank God for these Men and Women. USA all the way.”...

From the perspective of the American people, the principal attribute of this relationship is that it entails no real obligations or responsibilities. Face it: It costs us nothing yet enables us to feel good about ourselves. In an unmerited act of self-forgiveness, we thereby expunge the sin of the Vietnam era when opposition to an unpopular war found at least some Americans venting their unhappiness on the soldiers sent to fight it. The homeward-bound G.I. spat upon by spoiled and impudent student activists may be an urban legend, but the fiction persists and has long since trumped reality.

Today such egregious misbehavior has become unimaginable. Even if the wars in Afghanistan and Iraq are not especially popular or successful, no one blames the troops. Instead we cheer them, pray for them, and let them go to the front of the line when passing through airport security. And we take considerable satisfaction in doing so....

Americans once believed war to be a great evil. Whenever possible, war was to be avoided. When circumstances made war unavoidable, Americans wanted peace swiftly restored.

Present-day Americans, few of them directly affected by events in Iraq or Afghanistan, find war tolerable. They accept it. Since 9/11, war has become normalcy. Peace has become an entirely theoretical construct. A report of G.I.s getting shot at, maimed, or killed is no longer something the average American gets exercised about. Rest assured that no such reports will interfere with plans for the long weekend that Memorial Day makes possible....