You raise a good point. I have asked myself this several times, and I never found a satisfying answer. Fact is, that Japan didn´t surrender after Hiroshima, and that the Japanese military was ready to cut the throats of all allied POWs. They were just like the most desperate Nazis willing to let all their people die, because they realized they had lost anyway. While the bombing of Dresden really didn´t help to end the war, nor did it help to save allied lives, Hiroshima without a doubt did so.
I have come to the point to say that I can´t answer the question whether Little Boy should have exploded over the sea or an uninhabited island. It didn´t happen, Little Boy killed dozens of thousands. So it´s useless to answer this question. We know enough to avoid a 3rd use of nuclear weapons if ever possible, and that should be fine.
I'm sure Truman, like most of his advisors, simply assumed the atomic bombs would be used as soon they were ready. The only moral issue was ending the war by any means possible.
Gotta agree with ya on a 3rd. However, we did "test" out our latest MOAB and it had little effect on the hard core's.
We could nuke them and obliterate everything; it still wouldn't have an effect on the mind set overall. The "ROP" and their likes are in a "holy war" against anything that is not "them". The quicker we come to calling this "war" what it is, the quicker we can get it over with.