When you all get the chance, research the Mokusatsu Incident. I've brought this up before, but it raises intriguing - if not disturbing - alternate explanations regarding the decision to use atomic bombs.
I have my doubts about the legitimacy of attacking Japan in that matter. Remember I said "doubts", not "it was completely wrong and anyone who says otherwise is a warmongering monster". Dialogue on this issue continues in Japan, and their interpretation of the event is understandably quite different, but for a number of legitimate reasons. Japan is notorious for its revisionist tendencies in public schools and international relations, but I've spoken with members of the Japanese community on this matter, and willful opposition to the truth is not quite the case. This argument is difficult to gauge because its hypothetical nature raises complex dilemmas about conventional morality and our willingness to resolve conflicts as decisively as possible.
While Japan was by all means a real threat, I don't think it is a fair or conclusive assessment to simply say that we "knew for a cold hard fact" that the Japanese would fight with every man, woman, and child. Conflicting stories - or word on the street - suggests that the Japanese military leadership had been falling apart from the inside-out long before the US president gave his ultimatum. Civilian support of Japan's offensive against the United States had arguably been overestimated, as several sectors of Japanese society either grew apathetic to the national cause or genuinely frightful of US retaliation to further aggression on their part.
I recall watching a documentary called Black Light/White Rain that explores this topic in great detail. On one part (or in one of the extra scenes), a man who was part of the staff that organized the Enola Gay mission said the following in paraphrasing:
"In all the years that have passed, I've never lost a wink of sleep over the bombing of those cities. Not a single night of sleep lost. But I would never do that again, or wish that on anyone else. People keep talking about how we need to nuke terrorists and whatnot. No. If you really understood how a nuclear weapon works, you wouldn't want to use it."
Again, this is all from memory (but I'm sure as hell not making this up), and it may have been a different documentary, but this description puts the questionable justification of the bombing into greater perspective.
I honestly think we really can't push this debate toward its full potential without involvement of the Japanese, and I understand that this is a luxury to some degree.