This is a cherry tree photographed in Hiroshima 800 meters from the hypocenter of the first military use of a nuclear weapon.
Orac has a nice discussion of the decision to drop the bomb. I think he's right that, in the context of the massive firebombing of civilian populations, the decision to attack with nuclear weapons was probably not seen as controversial at the time.
The important thing about nuclear weapons isn't the power alone. The Hiroshima bomb killed fewer people than were killed by the firebombing of Tokyo or the bombing of Dresden, so the moral calculus would be easy for someone who authorized those attacks.
The bombing of Tokyo took 334 planes, Dresden used about 1200. Hiroshima involved a single plane, and produced comparable fatalities. That's a whole new calculus. It's hard to doubt that any thoughts of resistance collapsed when it became clear that a single American plane could do what would otherwise require hundreds of planes to be put at risk.
What I wonder, and I don't have a sure answer for this, is whether modern GPS targeted bombs obviate the need for widescale destruction. In WWII, precision bombing couldn't achieve the level of accuracy we can get today, and we can get that level of detail without worrying about exposing planes to ground fire.
Given those facts, is there any justification for deployment of nuclear weapons anywhere near civilian populations? Note that I'm not ruling out nuclear weapons or carpet-bombing of military targets, though the necessity for such power may be balanced by precision.
Then the question is, can conventional precision weapons be an adequate deterrent against a nuclear threat? I don't have an answer, but it's interesting to consider.