So it's not really "it's better that 200k Japanese civilians die than x US soldiers" (which is a despicable view and is based on the false views that massacring civilians is OK and that unconditional surrender was necessary), because they didn't know two bombs was the magic number. It could have been 10, or 50. Basically they were probably willing to kill a whole lot more civilians than they did.
Where "fight" means massacre civilians by the hundreds of thousands or millions. Where "won" means received unconditional surrender when they could already have a very favorable conditional surrender. Where "fight to survive" means they (the US in general and the US military, not individual soldiers) at this point (when they dropped the bomb) were in no danger of not surviving. Where "no time for philosophy" means no time for a conscience or morality.
And plenty of US military leaders at the highest levels did have a conscience and opposed using the atomic bomb against civilians at that point in the war. See my link in other comments.
It's important to recall that every nation's entire economy was subsumed in the war effort. American "civilians" wanted to kill Japanese; Japanese "civlians" probably hated Americans (there was a lot of racial prejudice in that era, on both sides).
Civilians may not have been combatants, but they were very much a part of the war machinery, and as such became a strategic target.
However this thesis runs into at least two problems:
The Soviets were no great threat to the home islands, at least without the naval oriented Allies providing ships, boats and air cover. Nor do I recall them showing any great interest in that decisive part of the end game, vs. playing the same game they'd started with Eastern Europe. Which, let us not forget, included mass murder of locals: https://en.wikipedia.org/wiki/Katyn_massacre
The Emperor mentioned the atomic bombing in his famous radio broadcast, not the Soviet invasion. (Very few other contemporaneous, reliable records survived the mass destruction of documents before the occupation.)
Few doubt that it was a cause of the invasion, but there's absolutely no support for it being a greater cause than the atomic bombings, with the promise of more to come.
The real effects of such weapons were unknown and the public opinion didnt really care about killing all those inocent civilians(it is not that different from the mass bombings done in the war, with "conventional weapons")
Committing atrocities in Nanking might not have been good PR, but I don't think it moved the needle like actually attacking America.
[1]: Source: my grandmothers' stories
I should of been more clear in that after the Red Cross photos, I doubt Americans could have thought less of the Japanese. I mean that in the context of when the Japanese started publishing head chopping contests of Chinese civilians between officers in the Imperial Army, no one in the US could be any more outraged.
I've been reading Now It Can Be Told by Leslie Groves, the Army general in charge of the Manhattan Project, and I just came to this bit in the chapter titled "Hiroshima", right after he delivered the first paper report of the bombing early in the following morning:
[US Army Chief of Staff] General Marshall expressed his feeling that we should guard against too much gratification over our success, because it undoubtedly involved a large number of Japanese casualties. I replied that I was not thinking so much about those casualties as I was about the men who had made the Bataan death march. When we got into the hall, Arnold [Army Air Force Commanding General] slapped me on the back and said, "I am glad you said that---it's just the way I feel." I have always thought that this was the real feeling of every experienced officer, particularly those who occupied positions of great responsibility, including General Marshall himself.
It was quite evident to all of us, as well as to the [War] Secretary up on Long Island [resting after the Potsdam Conference], that our hope of ending the war thought the development of atomic energy was close to realization.
In general, they of course knew they were doing a terrible thing, but as discussed here, it was to stop a much more terrible outcome. E.g. an estimated 250,000 killed every month the Greater East Asian Co-Prosperity Sphere. Or the mass use of nukes in the coming invasion; after Nagasaki a debate started about how to use the 3rd, to destroy another city or reserve it for the 5 or so needed for otherwise impractical Operation Olympic, the invasion of Kyushu (the Japanese had reinforced it, and had constructed way too many kamikaze planes, even more than we estimated).