H*LL No, not Nagasaki!!!
You know what, personally I see no problem with dropping atomic bombs on a target that was military in nature, but to drop them on civilians is just barbaric and low. It constitutes terrorism and violates the Hague Convention (regarding the rules of war) that the U.S. had signed. In this sense, the U.S. were no different to Nazi Germany and Japan when it came to war crimes on enemy civilians. At least with conventional bombing, bombers aim for specific military-related targets (like a barracks, munitions factory, depot etc), but the atomic bomb destroys everything even those not related to the war effort (think about hospitals, universities, high schools, primary schools, kindergardens, religious buildings, cultural landmarks, residential suburbs etc). Going behind enemy lines to bomb their civilians is low when there was a high concentration of Japanese military in Kyushu because they were anticipating a U.S. invasion.
The point is, are dropping atomic bombs on civilian cities ever justified for whatever political goal? Shouldn't the bombs have been dropped on a predominantly military target (like on the frontline)?
If a Nazi had dropped an atomic bomb on New York City, and he pleaded that he was merely trying to "end the war and save lives", would YOU still agree to him being hanged? If so, shouldn't Truman thus be hanged for using atomic bombs on civilian cities?
With no navy, no air force, their armies losing in China, their people at home starving to death, American bombers ruling their skies, an effective American sea blockade in place, Russia having just declared war on them, and with martial law imposed, Japan was essentially defeated by August 1945. America had 100% air superiority over Japanese skies and 100% sea superiority in Japanese waters. Japan didn't even have the ability to shoot down the lone bomber that carried the atomic bomb. No atomic bombs or a costly U.S. invasion was militarily necessary to end WWII.
If I was the U.S. President I would've waited until Russia declared war on Japan on August 9, 1945 (as part of the promise they made to America). I would've waited to see if Japan would surrender in the wake of this Russian intervention (Note: this is actually what happened, Russia's entry into the Pacific War was what forced Japan to surrender). I would've waited until Japan believed all hope in China was lost (which was inevitable with the Chinese winning the war and Russia's eventual invasion of Manchuria). I would've waited until the sea blockade forced the majority of the starving Japanese people and the nervous Japanese cabinet to end the war (this is what Fleet Admiral Chester Nimitz suggested to Truman, since he knew that with martial law imposed Japan was on the verge of rebellion). I would've given a public message to Japan saying that Emperor Hirohito would not be tried as a war criminal and the imperial family would be saved (this is what Gen. Douglas MacArthur wanted Truman to do, since he believed Japan only fought on to save the imperial family from post war prosecution).
These alternatives were there for Truman to use. It wouldn't of hurt to have tried them, but Truman did not use any of them. All these possibilities would've saved American lives, saved Japanese lives, given America a good image, and more importantly, ended World War II in a civilized manner. If Truman was serious about saving lives he would've tried those alternatives before resorting to the atomic bomb. It's funny how the atomic bombs were dropped on August 6 and August 9 when Truman knew that Russia would declare war on Japan on August 9. In an interview to "The New York Times" in 1946, Albert Einstein believed that Truman deliberately used atomic bombs to try and end WWII before Russia could get involved. And indeed, by looking at those dates the only logical explanation for Truman to drop the atomic bombs on civilian cities so close to Russia's intervention was to intimidate Russia.