I have wondered occasionally whether the US could have chosen a fortified island to demonstrate the bomb, and then said "Comments please?". Would the Emperor have faced his 'Coventry' decision and forced the US to prove they would drop it on civilians too?
From what I've read there was some talk of a demonstration, but it was a different world.
The propaganda forces used in wartime will cause all attitudes to polarise.
There wasn't enough fissile material for more than two or three bombs, and there was debate about whether the little boy design, which they were certain would go off, should be cannibalised for more fat men, which were much more complicated. The little boy design with a single point of ignition was much more dangerous to the users. They weren't using a tried and tested weapon.
Japan was finished on any rational basis, but after the Kamikaze attacks and the suicides at Okinawa etc., 100s of thousands of allied casualties were anticipated for the invasion of mainland Japan, not to mention huge numbers of Japanese. The US was fed up with Japan after the Pearl Harbour sneak attack and the suicidal defences. I've spoken to a few servicemen who were likely to have been involved in the invasion of Japan and they saw the dropping of the bombs as a divine deliverance
So much money had been spent on Manhattan that it had to be seen to be well spent, so the bombs had to be dropped and seen as decisive.
The Ruskies were talking about taking part in the invasion of Japan and the spoils and eyes were already turning to the post-war world.
No one knew how far the Japanese high-command's grip on information reached, so they might have chosen to ignore a demonstration on a fortified island and carryied on fighting because it was good for the soul. It's hard to say how much say-so the Emperor had as he lead a fairly closetted life.
So, all in all, some namby-pamby demonstration wasn't on the cards.
I believe Curtis Le May's incendiary raids, with a fire storm every time, caused more deaths, and leaflet drops warning of more to come, caused immense panic.
They razed 16 sq miles of Tokyo in a night.
No doubt he'll be along to tell us about it soon.