Firstly they only had two bombs and secondly but for the Emperor's intervention when he saw the results of the atomic bombs, they would have fought on. The Emperor or any Japanese General wouldn't have accepted an invitation to watch a trial run of a bomb. This sort of thing is fantasy for anyone who studied the Japanese psyche in WW2.
Secondly, "melting" a 100 thousand people or so is the lesser evil compared to the deaths of millions and the total destruction of the Japanese mainland and that's what it would have come down to.
Thirdly, if an atomic bomb had never been dropped who would have believed the effect of them and the Cold War might just have escalated to the Very Hot War but for the deterrent effect of having seen what the bombs did.
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