Warren Kozak writes in today's Wall St. Journal that on this, the 64th anniversary of the Hiroshima bombing, the historical event "has become a Rorschach test for Americans. We see the same pictures and we hear the same facts. But based on how we view our country, our government, and the world, we interpret these facts in very different ways."
While attempting to present a balanced argument, contrasting both sides of the debate, he clearly thinks that the risks of an invasion to American lives and the calculation that dropping the bomb would force a surrender were more than sufficient justification for the action. It's worth reading his whole argument.
But if the topic interests you and you're curious about the details of the war with Japan, how America's actions were rationally self-interested and thus some of the most moral in the history of war, and how Japan came to be one of the freest, richest countries on Earth mere decades after near total devastation, run, don't walk, to The Objective Standard and buy the article "Gifts from Heaven": The Meaning of the American Victory over Japan, 1945, by John Lewis. From the free bit you can see on the web:
The victory over Japan remains America’s greatest foreign policy success. Today, we take for granted a peaceful, productive, mutually beneficial relationship with the Japanese people. But this friendship was earned with blood, struggle, and an unrepentant drive to victory. The beneficent occupation of Japan—during which not one American was killed in hostile military action—and the corresponding billions in American aid were entirely post-surrender phenomena. Prior to their surrender, the Japanese could expect nothing but death from the Americans.
If there is one historical event that every American should study, beyond the American Revolution and the Civil War, it is America’s victory over Japan in World War II. Even more than the victory in Europe in the same war—in which we divided Germany with the Soviets—the victory over Japan remains the cardinal example of a complete, unambiguous, and fundamentally unshared American military victory.