"It is hard to imagine how many more GIs and Tommies would have perished in 1944-45 had Anglo-American leaders flinched from using all the means at their disposal to hasten the end of the war. Indeed, if the U.S. had staged a blood-drenched invasion of Japan while holding back its atomic arsenal, President Truman would have been indicted for that decision too."
Actually, per the History Channel, our invasion plan for Japan called for the use of atomic bombs to clear an avenue of approach for our invading force to follow into the interior of Honshu! They were oblivious to the dangers of radiation back then and our troops would probably have ultimately succumbed to the exposure too. So, we would have used more atomic bombs in the course of an invasion of Japan than we did.
What is little known is that there was a coup attempt by the senior generals in Japan at the end. They did not want to surrender and took control of the country/armed forces. They had no plans to surrender even after both atomic bombs were dropped!
Ultimately, a conventional bombing raid by the US in the NW part of Honshu serendipitously eliminated the leaders of the coup, control reverted to the emperor, and Japan surrendered.
Furthermore, the Japanese had plans to attack San Francisco with a radiological "dirty" bomb on August 17th, 1945. There is speculation that had they succeeded the Bay Area would be uninhabitable even today. Fortunately for us, the required radioactive elements (heh, heh) for the attack were coming on a U-boat from Nazi Germany and were surrendered to the US by the U-boat commander. This was only after Germany had surrendered and the Commander decided to not continue the mission.