There's only one country that has ever used a nuclear weapon.....maybe everyone should stop and think about that.
I don't want to make it out as if I defend the use of nuclear weapons (I mean, if all thing went my way, there'd be no war in the first place), but I think there's a practical, post facto defense of the using nuclear weapons to end the Pacific Front of WWII. Death tolls would almost have definitely been higher, especially for Japanese citizens, had the war continued. We can't pretend as if the alternatives were any better, as evil and horrible as Nagasaki and Hiroshima are, they're probably a pragmatically less evil options, at that point in the War.
The human imagination can be pretty good, but it's far, far from perfect. There's a power in actually being able to see
something in person. Nuclear weapons are as much a psychological weapon as much as anything. Carpet Bombing cities, and bombing something slowly, can lead to more deaths, but it doesn't let you see the entire effects of that at one go. Actually using the weapons, made humanity actually see the consequences. I'm not so sure that if nuclear weapons hadn't been used in Japan, they wouldn't have been used at some point between the USSR and the USA.
I don't think it's fair to blame the US for the results of WWII. And who do you blame exactly for WWII? Best answer I can come up with, is just humanity.
So ya, to tie all of that in with this thread, I really don't get the fear-mongering over Iran.