Sure, but I was questioning the premise (or rather the implied premise) in the OP, Jom. Grayling cites some of the arguments about the deployment ofthe bomb. One advisor, for instance, suggested dropping the bomb on an uninhabited island near Japan. He doesn't say why this suggestion was rejected. That Japanese militarism and its associated atrocities provide an unambiguous casus belli is a point I readily concede, but, in themselves, they should not inform, far less prescribe the means of ending it. Such is a practical question: how best to end the conflict? Grayling's point (obviously there will be historians who disagree with him - and I am not competent to adjudicate between the two views) is that: (a) bombing the cities wasn't necessary in the first place; and (b), even if it were, that the power of the bomb could have been demonstrated without immediate loss of civilian life.
Thanks to Saint Peter (never thought I'd hear myself saying that) for his question which reminded me of the Grayling debate (which also ihas the late Christopher Hitchens as a participant). Have just ordered the Grayling boook on the subject (Only £3 on Amazon).