[Ryzorian]

Unconditional surrender was the only way the US was going to go after Pearl Harbor , FDR knew that, an so did Truman. You pick a fight with us, you don't get to set "conditions" for when it stops. You think you can go into a bar and pick a fight with the biggest baddest guy in there and then somehow call it off with "conditions"? That's how that generation thought back then.

As to the emperor bit, we understood the importance of the emperor to the spirit of Japan, that's partly why they didn't try him as a war criminal. ( Not that we didn't get all the war trials we needed/wanted anyway) However, that came with a cavete, he had to give a speech at ground zero of Horishima. We made it a point that the emperor stayed emporer because we allowed it, based on our good graces, not because it was a condition we agreed to meet.

As to the question of morally justified? It shortened the war, so yes, it was.