Completely necessary. America had all but lost the will to keep on fighting after heavy losses in both theaters and incurring massive debt. It is my understanding that if the war was to go on any longer they would have called for a truce and offered Japan basically anything they wanted. The Japanese were not the nice, albeit fucked-up people they are today. If you think they were, google the Rape of Nanking. They were massive dicks to all the countries they occupied.
The bomb saved many lives in the long run, and also gave a demonstration of its power at a time when it was only a new tech. Imagine if they had left it a decade then dropped a few of the ones which are several hundred times more powerful. Hiroshima and Nagasaki gave people a reference point as to the destructive power of the nuke. Without that the Cold War could have been very different. Or the Korean war. Or Vietnam.
The bomb saved many lives in the long run, and also gave a demonstration of its power at a time when it was only a new tech. Imagine if they had left it a decade then dropped a few of the ones which are several hundred times more powerful. Hiroshima and Nagasaki gave people a reference point as to the destructive power of the nuke. Without that the Cold War could have been very different. Or the Korean war. Or Vietnam.