I would say the bombs were necessary to end the war. Every single Purple Heart medal issued since 1945 has come from a huge warehouse in Washington, DC where they are stored. They made over a million of the things in preparation for an invasion of Japan that never happened. They were expecting over a million casualties. They haven't had to make a new one since. They fully expected to have to kill every single Japanese man, woman, and child to end the war. The bombs rendered that unnecessary. Ergo, justified.