i think you are underestimating the Japanese aspect of it. The Japanese treated the Emporer like a god and they would have defended him till the death. Millions of Japanese and American soldiers were saved. The island battles in the Pacific were very deadly and Truman didnt want more of that so he did what needed to be done.
I think you should read more on this subject.
See this site of quotes by leaders of the era:
http://www.doug-long.com/quotes.htm