No sympathy for those making the decision follows from any of it. Truman et al knew what they were doing and are morally responsible for their actions. They did not pursue every diplomatic avenue to avoid continued killing because their prestige was more important to them, and probably because it didn't occur to them that it mattered that much to the Japanese, and probably because they hated them as enemies and had not yet adopted the magnamity shown by MacArthur after the war, when he decided the emperor should stay. They wanted to break wills and thought that was the only way to peace. That is an easy thought but it is also easy to see that it is false.
Plenty of third parties saw the unconditional surrender demand as prolonging the war to little purpose. Few probably knew its important at the close of the war in Europe for keeping all the allies on the same page instead of bickering with one another or negotiating anything with the Germans, and it was useful in that context. It was superfluous with Japan.
And it worked SO well in World War I . . . .
Sorry. It's all 20/20 hindsight and second guessing, fueled in large part by those who find America at fault for every decision ever made back to the Jamestown settlement. We have the Apologist-in-Chief in the White House right now -- all you're doing is encouraging him.