I have read that the American POWs would have been killed when the US had invaded the home islands. (I know one of them personally--still alive at 92 or 93.) My father would have had a good chance of being one of the Americans killed in the invasion. He never doubted that using the bombs was the right decision.
This was all about Obama getting to preen--looks like this was before he knew he was going to be awarded the Nobel Peace Prize for his great achievement of not being George W. Bush.