Are mass exterminations of civilian populations now acceptable, if that is "cheaper" than other ways of winning? How about Gaza? Perhaps Israel would then be justified in exterminating everybody in the entire territory, just because Hamas refuses to surrender. It's plain it would cost the Israelis dearly if they had to go into Gaza and militarily take Hamas out one by one.
I suspect you haven't thought your view through.
Most everyone in the world would think that it was an absolute atrocity if Israel were to exterminate the entire population of Gaza. However, when the Americans did it in Japan, it was ok? If it's wrong in one case (and it is wrong) it is wrong in both cases.
The Americans did not eliminate the entire population of Japan, Hiroshima or Nagasaki. Why do you feel the need to mislead?
The question at the heart of this debate, which you refuse to even think about because it makes you look dumb (again) is if one believes that the killing of X civilians, will save the life of 10X civilians and 3X soldiers (just to make up numbers) is doing so:
a) a war crime.
b) morally incorrect.
The answer, while not simple, is one that I think most rational people can agree upon.