You should really argue whether or not the entire war was justified from the american/japanese point of view.
The war in the east was really rather pointless, but america really had no choice but to go to war after being attacked by japan. They couldnt afford to lose face, and had to make clear that they would not tolerate being attacked.
Anyway, the japs had loads of inhumane POW camps, so they wern't exactly innocent either.
Still, the nuking of a civilian population was not moral, but nor is it moral for any civilian population to be bombed. All of the big countries (except USA) got heavily bombed anyway, so i dont see how being nuked is so much more inhumane.