I think everyone here is forgetting one important thing, and i hope this hasen't been mentioned before because i haven't read through this whole thread yet. But remember that soldiers and civillians really are the same thing, i'm pretty sure there was a draft during WW2. So many soldiers diddn't choose to fight, but had to. I'm sure most of the drafted soldiers didn't want to fight, same for most civillians. So my point here is invading Japan would have been the same as forcing people (drafted US soldiers) to their death, or killing them.
Also i think maybe some people should lighten up here and not take some things so seirously. Yes using nucelar weapons on ANYONE, civillans or soldiers is very bad and should not be done. But i really truly don't care what happened around 60 years ago, call me a heartless bastard if you want, but it happened for a reason, and if there were a good enough reason for it to not happen, then it probably wouldn't have.