Truman might the right call, it shouldn’t even be open to question. Upwards of 1 million US casualties alone to cover the butts of the Japanese aggressors? No thanks. God bless Truman, the last decent Democrat.
War is requires the ultimate cruelty and cannot be sanitized or made humane if one seeks to win. The most humane thing one can do is to end the war quickly as possible with the means at hand.
What is the difference if the enemy dies by bullets, (nuclear) bombs or fire? The object of war is to impose one’s will upon the enemy and make their lives so insufferable as to break their will to continue further resistance.