Dr. Bryan Caplan makes a compelling argument, by asking some very uncomfortable questions. A good (and brief) read worth your time.
Tell Me the Difference Between My Lai and Hiroshima, Bryan Caplan – Library of Economics and Liberty: In the My Lai Massacre, a company of American ground troops killed between 347 and 504 unarmed Vietnamese civilians in a village suspected of harboring Communist guerrillas (the VC). After the massacre became public knowledge, Captain Ernest Medina denied giving orders to kill women and children. But some platoon leaders testified (without plea bargains, as far as I can tell) that Medina had explicitly ordered them to kill every living thing in the village.
In Hiroshima, the American crew of the Enola Gay killed 90,000 to 166,000 people in a mid-size Japanese city with an atomic bomb. According to the best estimate I could find, about 12,000 of the dead were Japanese soldiers. The rest were unarmed civilians. No one disputes that the Enola Gay’s crew was following orders.
The My Lai Massacre is now almost universally considered a heinous war crime. The Hiroshima bombing, in contrast, enjoys bipartisan admiration. What moral distinctions might you draw between the two?