Allied casualties were expected to be in the high hundreds of thousands. (https://en.wikipedia.org/wiki/Operation_Downfall)

That is true. I was not there and im of a completely different world. Well, to be honest i ended up agreeing atleast partly too. For context im from europe, and a small country arrayed against a historically and currently aggressive and strong neighbor, aaand i was conscript officer in charge of a few hundred men total. Believe me that im not that detached from this question, however my concience about bombing civilians is also quite conflicted but heavily leaning towards the Geneva Conventions.

In conclusion; no, i dont agree that it was be "perfectly ethical" or even simply ethical, but rather a neccesity born of the lack of efficacy in the firebombing campaing. And yes, a top-down hierarchical militant society like imperial japan of the time would not have surrendered without significant show of power, of imminent destruction, demonstrated. Im personally more convinced that Hirohito only issued the decree to surrender unconditionally due to the fear of imminent destruction of the capital, since a military society would always expect an attack on the command structure.