If he said that on August 2nd, he had at least 4 days to contact the US and make a goddamn decision.
Maybe they weren't his to sacrifice, but that wasn't going to stop him from sacrificing them. They were warned. We dropped pamphlets announcing an attack and warning the people to evacuate major cities before the bomb was dropped. It was a hell of a lot more than their emperor ever did for them. Our only other option was invasion. They would have died just as quickly then, and they would have taken thousands of Americans with them. It was better them than us.
I built a bomb. I didn't drop it. But if I were looking at dropping a bomb or invading Japan, I'd have made the same call.