If any documents were ever created about this debate, they've probably been destroyed, and those involved have taken it to the grave with themselves. So I suppose technically we can never know for sure. But I think the cynical view is far more well supported. Or at least I think the cynical aspects were the majority of the logic behind it. And it was not only about control of Japan but also about sending a message to the USSR as the US undoubtedly saw the outlines of a new West-East world order emerging after WW2. And all the way up until the 80s [1] our dominant political philosophy was that we could win by intimidation and demonstrations of force, nuclear in particular.
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Wow, loving LLMs when digging into topics now a days. GPT was able to direct me to Truman's diary entries which are public record. [2] I take back the weasel wording above. Truman himself was quite clear on his intention and desires:
"Discussed Manhattan (it is a success). Decided to tell Stalin about it. Stalin had told P.M. of telegram from Jap Emperor [actually from the Foreign Secretary] asking for peace. Stalin also read his answer to me. It was satisfactory. Believe Japs will fold up before Russia comes in. I am sure they will when Manhattan [A-bomb] appears over their homeland. I shall inform Stalin about it at an opportune time."
- President Harry S. Truman, July 18th 1945
[1] - https://en.wikipedia.org/wiki/Proud_Prophet#Impact
[2] - https://nsarchive.gwu.edu/document/28466-document-47-trumans...
That was particularly painful for Churchill to accept at the end when he had to hand over Poland to Stalin. Poland was the reason Britain officially entered WW2 in 1939
https://en.wikipedia.org/wiki/Western_betrayal
> We and France are to-day, in fulfillment of our obligations, going to the aid of Poland, who is so bravely resisting this wicked and unprovoked attack upon her people. We have a clear conscience. We have done all that any country could do to establish peace, but a situation in which no word given by Germany's ruler could be trusted and no people or country could feel themselves safe had become intolerable. And now that we have resolved to finish it, I know that you will all play your part with calmness and courage
(Chamberlain, Sep 3, 1939)