Using it today would save even more.
I read a once that there was also a plan to use atomic bombs to blow breeches in the Japanese defenses for Allied troops to pour through into the countryside.
It would have been a tragedy to have our troops march through a radiation zone on their way to battle.
ping for later
It is never right to do a wrong thing in order that good may result.
It is OK to kill an invader. Bombing the invader's mother, father, grandmother and grandfather doesn't sound like killing an invader.
Bombing munitions factories is generally seen as a normal part of a war.
Looks like it is not possible to say that "bombing saved lives".
There would be no Japanese culture left and that territory would probably have been annexed by the US considering how much blood we paid for it.
With American forces locked in combat in the south of Japan, little could have prevented the Soviet Union from marching into the northern half of the Japanese home islands.
Russia would never have been able to do that considering that they could not effectively project power across the ocean.
Other factors that influenced the decision to drop the bomb were:
a) Inadvisability of "Demonstration": one plan was to invite the Japanese and neutral observers such as the Swiss to a demonstration of the bomb at sea near the coast of Japan. This was decided against because we had only tested one bomb. It was not at all clear that these weapons would work reliably every time and if we set up a demonstration and it didn't go off we would have lost 'face'.
b) The Horror of Blockade: Another option to avoid the loss of American lives was to blockade Japan until they surrendered. This was dismissed because a) it could take many months or even more than a year and we wanted the war over with and b) the brunt of the blockade would be borne by the elderly, the young, the sick and civilians - whatever food and medical care was available would of course have been given to the Japanese forces.
c) The Number of Bombs: IIRC after we dropped the two we had enough material to make one more by September and one more by December. After that my memory fails me but I want to say that we could only make maybe one or two a quarter (anyone have any data on that?) In any case, this also influenced the decision not to have a 'Demonstration'. We had two bombs, if we used one in a 'Demonstration' we only had one left and another one available in September. We didn't know at the time what the reaction of the Japanese would be.
I'm sorry I can't give sources for this but my library is not readily accessable.
I am also one of those who wouldn't be here if the bombs hadn't been dropped. My father, God rest his soul, was in the USN Medical Corps on an LST (one of the ones in a flotilla that converted to a hospital ship with the OR on the tank deck). He had been at the invasion of Okinawa and they were slated for the invasion of Japan. He never would have come back.