We were already utterly destroying Japanese cities with fire bomb attacks, with loss of life in single attacks equivalent to or even higher than when the A-bombs were used.
The A-bombs were harbingers of greater terrors to come, but their use at the time provided no killing power that wasn’t perfectly available via other means.
It there really any moral difference between killing 100,000 people with tens of thousands of bombs dropped by 1000 planes, or using a single Bomb dropped by a single plane?
The purposes of dropping the bomb(s)were were multifaceted, the psychological effect it was meant to have was at least as important as the military strategy.
View this declassified Document.
Minutes of the second meeting of the Target Committee
Los Alamos, May 10-11, 1945
6. Status of Targets
A. Dr. Stearns described the work he had done on target selection. He has surveyed possible targets possessing the following qualification: (1) they be important targets in a large urban area of more than three miles in diameter, (2) they be capable of being damaged effectively by a blast, and (3) they are unlikely to be attacked by next August. Dr. Stearns had a list of five targets which the Air Force would be willing to reserve for our use unless unforeseen circumstances arise. These targets are:
(1) Kyoto - This target is an urban industrial area with a population of 1,000,000. It is the former capital of Japan and many people and industries are now being moved there as other areas are being destroyed. From the psychological point of view there is the advantage that Kyoto is an intellectual center for Japan and the people there are more apt to appreciate the significance of such a weapon as the gadget. (Classified as an AA Target)
(2) Hiroshima - This is an important army depot and port of embarkation in the middle of an urban industrial area. It is a good radar target and it is such a size that a large part of the city could be extensively damaged. There are adjacent hills which are likely to produce a focussing effect which would considerably increase the blast damage. Due to rivers it is not a good incendiary target.
(Classified as an AA Target)
(3) Yokohama - This target is an important urban industrial area which has so far been untouched. Industrial activities include aircraft manufacture, machine tools, docks, electrical equipment and oil refineries. As the damage to Tokyo has increased additional industries have moved to Yokohama. It has the disadvantage of the most important target areas being separated by a large body of water and of being in the heaviest anti-aircraft concentration in Japan. For us it has the advantage as an alternate target for use in case of bad weather of being rather far removed from the other targets considered.
(Classified as an A Target)
(4) Kokura Arsenal - This is one of the largest arsenals in Japan and is surrounded by urban industrial structures. The arsenal is important for light ordnance, anti-aircraft and beach head defense materials. The dimensions of the arsenal are 4100' x 2000'. The dimensions are such that if the bomb were properly placed full advantage could be taken of the higher pressures immediately underneath the bomb for destroying the more solid structures and at the same time considerable blast damage could be done to more feeble structures further away.
(Classified as an A Target)
(5) Niigata - This is a port of embarkation on the N.W. coast of Honshu. Its importance is increasing as other ports are damaged. Machine tool industries are located there and it is a potential center for industrial despersion. It has oil refineries and storage.
(Classified as a B Target)
(6) The possibility of bombing the Emperor's palace was discussed. It was agreed that we should not recommend it but that any action for this bombing should come from authorities on military policy. It was agreed that we should obtain information from which we could determine the effectiveness of our weapon against this target. B. It was the recommendation of those present at the meeting that the first four choices of targets for our weapon should be the following:
a. Kyoto
b. Hiroshima
c. Yokohama
d. Kokura Arsenal
C. Dr. Stearns agreed to do the following: (1) brief Colonel Fisher thoroughly on these matters, (2) request reservations for these targets, (3) find out more about the target area including exact locations of the strategic industries there, (4) obtain further photo information on the targets, and (5) to determine the nature of the construction, the area, heights, contents and roof coverage of buildings. He also agreed to keep in touch with the target data as it develops and to keep the committee advised of other possible target areas. He will also check on locations of small military targets and obtain further details on the Emperor's palace.
7. Psychological Factors in Target Selection
A. It was agreed that psychological factors in the target selection were of great importance. Two aspects of this are (1) obtaining the greatest psychological effect against Japan and (2) making the initial use sufficiently spectacular for the importance of the weapon to be internationally recognized when publicity on it is released.
B. In this respect Kyoto has the advantage of the people being more highly intelligent and hence better able to appreciate the significance of the weapon. Hiroshima has the advantage of being such a size and with possible focussing from nearby mountains that a large fraction of the city may be destroyed. The Emperor's palace in Tokyo has a greater fame than any other target but is of least strategic value.
I agree that it had great psychological impact, giving the Japanese military the excuse they needed to quit.
But from a moral perspective the difference seems like that between killing several people with a pistol or a grenade. Doesn’t make much difference to the victims.