Read up on the Okinawa campaign and how costly that was. There was no indication that the Japanese would have surrendered without the bombings of Hiroshima and Nagasaki and the invasion of Japan would create a much higher potential loss of military and civilians on both sides. Morally there is no difference between a nuclear bomb and conventional bombing. Dead is dead.
The bombing of Hiroshima and Nagasaki had the effect of saving the Japanese from themselves. They were preparing to have civilians attack the invaders with pitchforks, spears and machetes. Imagine how that would have gone. The "they would have surrendered without the bomb" argument is a more recent one. The U.S. expected to be fighting into 1946 and so did the Japanese. The loss due to starvation would probably have exceeded military losses.
The moral issues on the bomb came up after the war. Particularly when we realised there were enough bombs to wipe out humanity, and still are. Also, there has been a lot of whitewashing of the Japanese since the war. If you read up on their actions in China and the Pacific you will probably feel a lot less sorry for them. Their humanity was severely lacking. Luckily it is a different story today. But the Japanese do not fully acknowledge what they did in the war and a lot of the history is not taught to the young. This contrasts with Germany which basically acknowledged what was done and set about purging it from society. That is not the Japanese way, though.