I disagree. After dropping the bomb on Hiroshima, we warned Japan again that we would drop another A-Bomb if it didn't unconditionally surrender. Japan ignored our warning. So if Japan refused to surrender after we wiped out 80,000 people with one bomb, what makes you think they would have surrended if we had blown off the top of a mountain without killing anyone? (The only logical answer is that Japan had more repsect for mountains than for people, which is why an invasion of Japan would have resulted in millions of casaulties.)
First of all, we had the information that the Japanese were already trying to find terms of surrender through diplomatic channels via the Russians, who at that point had not declared war on Japan.
Second, we knew that the major sticking point on "unconditional surrender" is that they did not want the Emperor/god himself tried for war crimes. And that's an assurance we could have given them: he was not, in fact, put on trial after the war.
Third, this every-faithful-Japanese-with-a-sharpened-bamboo-stick island-by-island defense which we anticipated, was predicated on their religious belief in the utter sanctity of Japanese soil, in particular Mt. Fuji. If Mt. Fuji had been destroyed, it would not just have been an awesome geological phenomenon. It --- arguably -- could have broken the psychological hold of their fanatical national/paganism.
Neither of us have clairvoyant powers. I am just saying that there is evidence that other options were available. Again I reference the Alperovitz book. And many of America's military leaders --- some of whom were rather sharply critical of FDR and Truman and their left-Democrat civilian advisors --- thought the same.