Was the American populace against it or did it see it as a way to end the war quickly? How about other countries?
I gave a response on this question from a dutch point of view (and also small coverage of the Vatican and some hints of the Brits) useing newspaper archives
All in all it seemed that the implications where very well understood, I was surprised about how much of the social implications where being discussed on the first newspaper edition after the first bomb (and over the fews days after that). Check my link to see my (lenghty) response.
I found this thread from a while back that directly addresses your question: