On August 6th, in 1945, the world saw the first use of atomic weapons against human targets. On this day 63 years ago, humanity lost its nuclear virginity. Until the end of time we will be a species that has used fission bombs in anger.
Time has passed, and we still haven't blown up our world, despite a close call or two. Which makes it difficult to criticize the decision - would things still have turned out all right, if anyone had chosen differently, anywhere along the way?
Maybe we needed to see the ruins, of the city and the people.
Maybe we didn't.
There's an ongoing debate - and no, it is not a settled issue - over whether the Japanese would have surrendered without the Bomb. But I would not have dropped the Bomb even to save the lives of American soldiers, because I would have wanted to preserve that world where atomic weapons had never been used - to not cross that line. I don't know about history to this point; but the world would be safer now, I think, today, if no one had ever used atomic weapons in war, and the idea was not considered suitable for polite discussion.
I'm not saying it was wrong. I don't know for certain that it was wrong. I wouldn't have thought that humanity could make it this far without using atomic weapons again. All I can say is that if it had been me, I wouldn't have done it.
The Second World War, as a whole, was probably the most catastrophic event in humanity's recorded history. The world was pretty much screwed as soon as it started -- indeed, probably as soon as Hitler acquired control of Germany.
For the purpose of saving humanity in the future, it may not be most effective to focus our attention on particular decisions (even apparently large ones) made during the course of the war (indeed, near the end of it); we risk missing the forest for the trees.