I was 23 once

Jimmy Carter was President.
I think the dropping of the atomic bombs on Hiroshima and Nagasaki (plus the invasion of Japanese-held Manchuria by 1.5 million Soviet troops the same week) was the only thing that could
shock the Japanese military into surrendering.
Now imagine that Truman had not authoised using the bombs. We would be here debating “was it moral for Truman to allow 5 million US and 20 million Japanese deaths during the invasion (just picking numbers here) when he had the means at hand to end the war right away?”
HST was also no doubt looking past simply defeating the Japanese. The USSR was our ally at the time and our deal with them was that once Hitler was defeated they would help us with Japan. If we invaded, they would have been there too. Korea would be all Communist and there might be a North and South Japan.
Lastly, the use of the bombs caused a change in the Japanese psyche, a rejection of militarism that a conventional loss would not have brought about.
I don’t know if one can say the use of the bombs was moral or not – but it was militarily and politically correct and certainly prevented a great deal of evil.