The thing is, the nuke was deliberately used against civilian targets, which violates all codes of conduct of a war. Deliberately bombing civilians is an act of terrorism. Of course at the time, there were no rules, so we needed this war to get the rules into place.
Now we have the SALT II treaty, Geneva convention,
Link to Salt 1
Link to SALT 2
The Geneva convention
War is much more civilized now... coming from civilized nations.
I'm afraid that any way you look at it, using the nukes was bad. The only reason that it was allowed or that there were no repercussions, is because there were no rules at the time regarding the use of such weapons, and in times of war, anything goes. We did make up for some of it with the aid that we have provided Japan, and with the protection, but that was only out of a sense of having to make amends for the damage caused. The USA was otherwise not accountable for using a nuclear weapon.