Your math is a bit off for a two month blockade tops. I said drop one, not a dozen, in a remote location as a demonstration. At no point have I advocated an invasion. I said we should be better than that, not that we were.
Make no mistake, I understand the fact of how you kill them is largely irrelevant. We will leave aside the ramifications of the radiation from an atomic bomb for the purposes of this point, or you can simply fold them into casualties, whichever.
The point I am making is how it was perceived. This perception of outrage over a new technological terror is nothing new. I can point back to at least the crossbow. So tell me, since this has been going on for hundreds of years at least, why didn't we realize how this would be perceived? Bit more dangerous than a crossbow. If we come up with an uber weapon that can destroy anything within a thousand mile radius and selectively, would we be technological cave men and not understand how the use of the weapon would be perceived?
As to whether it would have worked? Maybe not, but again, we would have tried. Hirohito was already indecisive at best about the war by this point. He was hoping for something to use at the negotiation tables. Since the idea of a demonstration pushes back everything a couple of months (being generous with that figure since you said my source was incorrect) the Russians would have already attacked in all likelihood. This sustained attack would have brought even more pressure for an unconditional surrender. Which is all we should have accepted btw.
As to the firebombings, when the war was going full force and we hadn't won all but completely, I can understand it. I do think intentionally targeting civilian populations is wrong, but war is war.