The two bombs saved a million lives.
I think that number is conservative!
Among others, the bombs saved an estimated 300,000 Allied POW's who were ordered to be executed the minute an invasion was launched.
Let us also not forget the Japanese were working on their own weapons of mass destruction -- primarily biological -- through facilities such as Unit 731. There is virtually no doubt this horror would have been unleashed on the United States had the Japanese been able. The bombs prevented that tragedy.
R. J. Rummel, a professor of political science at the University of Hawaii, states that between 1937 and 1945, the Japanese military murdered from nearly 3,000,000 to over 10,000,000 people, most probably 6,000,000 Chinese, Indonesians, Koreans, Filipinos, and Indochinese, among others, including Western prisoners of war. This democide was due to a morally bankrupt political and military strategy, military expediency and custom, and national culture." According to Rummel, in China alone, during 1937-45, approximately 3.9 million Chinese were killed, mostly civilians, as a direct result of the Japanese operations and 10.2 millions in the course of the war.
Finally, it should be remembered the bombs put an end to other Japanese atrocities, beyond comprehension to most and too numerous to list.