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.
Seconding Scott Aaronson (especially on the tragedy of the US getting nukes too late) and Michael G R, though with the suggestion that the "demo" bomb could have been Trinity.
Eliezer: I think that the hypocrisy of the US is mostly in our maintaining a large arsenal but telling others that they can't have any, not in having used nukes. I don't see a case for .1% probability increase for nuclear war without using the bomb which is stronger than the case for the inverse, but I do see a million dead Japanese. Also, in terms of catastrophic risks, a couple more years of total war to encourage ultimately disastrous cultural changes in the US.
What I really want to know about WWII is why Hitler wasn't assassinated before it was too late. Surely if the situation with Archduke Ferdinand teaches us anything it's that Assassination can solve all of one's geo-political problems ;-(