There have been a couple of threads on this topic over the past few years, and I'm not sure I want to get involved again. I'll state my point of view, but I don't expect to change the minds of any of the nuke lovers, and they certainly won't change mine.
In any case, the way I view it, the A-bombs that were dropped on Hiroshima and Nagasaki were weapons tests on live subjects, a conclusion to the Manhattan Project. As I've said before, look at the timing of the dropping of the bombs. The bombs were dropped in early August while the invasion of Japan was not scheduled until November, months later. Why the ungodly haste to drop them? Because the Americans might lose their opportunity for the weapons test if the Japanese surrendered. Also, why drop the second bomb? Surely the difference in psychological impact of eliminating one city or two cities (in the context of a bombing campaign against many cities) was minimal. Well, the Americans had two different kinds of A-bombs, and they wanted to test both.
Second, it was a demonstration to the Soviets of the new weapon that the US had. Ending the war was not the primary motivation for dropping the bombs.
There are a number of fallacies that those in favour of the dropping of the bombs typically trot out (and have done so here). The first is that the Japanese atrocities against their defeated foes justified Hiroshima and Nagasaki. The way I see it, nothing justifies an atrocity. A second fallacy is, "If they did it, it was an atrocity, but if we did it, it was necessary". Nope, both are atrocities and both are evil. The third fallacy is that dropping the bombs ended the war and saved lives. Hasegawa's thesis, cited by the OP, is interesting and makes some sense. Regardless, the US haste in dropping the bombs showed a recognition that Japan was close to surrender, and belies that third fallacy.
