The generally accepted reasoning behind that bombing is that thousands of United States troops would have died in a protracted war and a clear message had to be sent. Regardless of how one assesses the issue, the fallout, no pun intended, from Japan's choice was massive.
Depending on how one perceives Weinberg, he did cover all of the normal bases but perceptions of his worldview may lead some to believe that he did not. After all, some may view Truman's choice to bomb Japan as heroic and proper while others may view it as tragic and vile even with the attack on Pearl Harbor and the aggregate actions of both Japan and Hitler over World War II up to and including the Holocaust. No matter how noble and academic someone may seem or portend himself/herself to be, worldview and historical perceptions almost inevitably color the research, perspective and findings of history. The cliche is that the winners of wars write history books but to say that historical analysis is monolithic would...
Even academic journals that are supposed to be peer reviewed and unbiased are bereft with opinions and points-of-view that are clearly biased and skewed in one way or another and it is often clear what motivates such bias. Nevertheless, while Weinberg's perspective is certainly useful, other perspectives would also be instructive and should be consulted as well. it's always good practice to get all sides of an argument anyway.
Notes
(1) "Modern History Sourcebook: The Molotov-Ribbentrop Pact, 1939." Fordham.edu. http://www.fordham.edu/halsall/mod/1939pact.html (accessed September 12, 2012).
Bibliography
Keegan, Richard. The Battle for History: Re-Fighting World War II. New York: Vintage Books, 1995.
Overy, Richard. Why the Allies Won. New York: WW Norton & Company, 1995.
Weinberg, Gerhard. A World at Arms: A Global History of World War II. Columbia: Columbia University Press, 1994.
