Ditto my grandfather. He didn't see a problem with dropping the bomb. "They started it, we finished it, and I was glad not to need to go there after a year in Europe.", was his attitude, approximately.
I read a little about Operation Olympic. The spearhead - (if memory serves) the 4th and 6th Marine divisions - were written out of the plan by H+36 because it was assumed they'd cease to exist. Dropping the bomb had a terrible cost, but all other alternatives were worse.
Operation Olympic had an order of battle of 14 divisions at landing. Operation Coronet had 25. By contrast, Operation Overlord in Normandy involved 12 divisions.
Generally, after you read up on the planning invasion of Japan....you see a campaign that takes a minimum of two years and costs a minimum of 100,000 American lives. Few would guess the Japanese civilian toll....but it has to be a minimum of half-a-million dead from starvation or being used as shields for the military leadership.
An alternate war would easily be written with WW II ending sometime in 1948. There would have been no will left in the US for rebuilding Germany or Japan by that point.