Was it necessary to drop the atomic bombs "fat man" and "little boyon Hiroshima and Nagasaki?

Pro side:
The two atomic bombs had successfully saved more lives for the Americans and Japanese military without any invasion of the mainland. It finally ended WW2 in 1945 and did not allow Soviet troops to invade Japan.

Con Side:
Many civilians in both cities had instantaneously died by one bomb and many more died by radiation poisoning. Japan was already going to surrender soon due to the fear of the communist threat in the east. United States took this opportunity to bomb Japan and scare the Soviets for the upcoming Cold War.