I got to page 6...then it was just too much.
I have read arguments on both sides. Some are good, many are bad. Perhaps the biggest problem I have with all of the responses is that they show a clear lack of research into the subject. I don't completely blame the people for that; much of what I know on the subject I learned not by actively searching but by simply reading books on WWII. I won't pretend that I have every single angle, but I do hope that I have a more comprehensive view than what I've seen here.
First off, however, I should make this clear: Anyone who makes any kind of distinction that puts America as the "good guys" and Japan as the "bad guys" is at best misguided. I was one of these until very recently. Part of this is perspective. Most of the soldiers on all sides were "good guys," people fighting for what they believed in, whether they thought they were protecting their homes or fighting for the glory of the Fatherland. Then there's the fact that the Western Allies were allied to, and turned a blind eye to the known crimes of, the world's most powerful villain, Joseph Stalin. Never forget that at the behest of Stalin and his underlings, the Soviet Union achieved a scale of wholesale slaughter that the Nazi's could only dream of. It is a sobering thought that the Soviet Union could have won the entire war by themselves. (don't get into Lend-Lease, they were winning before that got going)
So, we've already established that America was at best the "anti-heroes" of the second world war; fighting for a good cause, but willing to deal with Satan himself in order to do it. Now, for the bomb...
First, while the Japanese may have been trying to surrender, they were not doing it the way the Allies insisted. The Japanese believed what many Nazi leaders held onto in the final days of the war in Europe: they could achieve a peace that would allow them to keep most of their remaining territory. The Allies made it clear that this was not acceptable. The last time Germany had kept its territory, it had succeeded in launching the second world war. From what I've read as well, the Japanese may have wanted to surrender (though I really doubt this), but they needed an excuse. Their twisted version of Bushido warranted that they keep fighting as long as they are able. The atomic bombs gave them an honorable way to exit. What can you really do to fight something like that before SAMs, heat seekers, and other high-tech devices?
Now, the U.S. did consider different ways of demonstrating the bombs power. None were considered as effective as a live demonstration.
The bombs were indeed deterrents against the Soviet Union, but that was really more of a bonus. We did, after all, ask the Soviets to enter the war. Roosevelt was willing to sell out Eastern Europe to do it.
Someone mentioned that numerous generals and admirals in the U.S. military believed the bombs unnecessary. This is because most of them believed that the war could be won simply by a sustained air offensive, a naval blockade, a ground invasion, or some combination of the three.
Air power couldn't work, because it wasn't showing any results anymore outside of more cinders on the ground. As the Germans succeeded in doing, the Japanese responded to the bombing of their cities and factories by spreading their industry out and concealing it. To Germany's immense credit, they managed to constantly maintain or increase production in all sectors until 1944. The Japanese didn't do as well, but they still pulled off something similar. What's more, strategic bombing was a result of the technology at the time, and proved to be very ineffective. When the Germans bombed Britain, the British simply fought harder. When the Allies pulverized German city after German city, the Germans simply got right back to work and toughed it out. The Japanese did the same thing. There's a reason armies don't use strategic bombing anymore (besides the foolish negative press and civilians). Like artillery, strategic bombing may demoralize some, but for the most part just pisses off the targets. A modern day example can be the hornets nest that the 9/11 attacks stirred up. Sure, America screwed up what it could have done with that fervor, but while the attacks frightened Americans, that only lasted about a day, then they got mad as all Hell.
Naval blockades were pointless, because we'd already been doing something similar. For 2-3 years, our submarine force had been wreaking havoc on Japan's merchant marine fleet. Stopping the last few ships would have made little difference.
A ground offensive, as we all know, would have led to atrocious casualties for all involved. The Japanese fought savagely enough on Iwo Jima and Okinawa, the first bits of Japanese soil the U.S. invaded. The civilians at Okinawa committed mass suicide to avoid the Americans. That was the power of Japanese propaganda. It would have worked in the home islands.
Besides that, all of these would have had high financial costs, allowed the Soviet Union legitimate claim to more Japanese territory, and allowed Japan's main army (which America never faced in combat, mark you) to continue fighting in China. It would have also taken our attention away from the crisis in Europe, where millions were starving, and communism had a real chance to gain significant ground in many countries outside the Soviet bloc.
As for choice of targets, both Hiroshima and Nagasaki were completely legitimate military targets. Hiroshima was home to the Japanese Second Army and Chugoku Regional Army, and as such was a military depot. Nagasaki was a major port, military and commercial. In addition, warnings were indeed issued, repeatedly, both over radio and in the form of leaflets, telling the Japanese that they'd best get away from their cities. The warnings were ignored by the government, which kept those civilians who did believe inside the cities.
...a cripes. Spent so much time on this I've actually forgotten the rest of it...ah well, I'll add more as things move along.
Anyway, my point is this. The bombs, both of them, were completely necessary. They spared millions of lives, not just Japanese and American but Soviet, Chinese, and many others as well. They were the quickest, most efficient way of ending the war. The facts leading up to it speak in favor, as do the results. Anonymouse, I believe, stated his/her belief that the Japanese SHOULD have been eradicated; that the only way to truly achieve victory is to wipe your opponents out with everything you've got. I do agree that overwhelming force should always be applied. If your opponent slaps you in the face, you should knee him in the groin and beat him unconscious. Break a few limbs for good measure. But history speaks overwhelmingly against having to wipe out your enemies. The fates of Germany and Japan alone speak volumes against their destruction: 63 years after the end of the war, Germany is second only to Russia as Europe's most powerful state economically and militarily. Japan is the 2nd and 3rd largest economy in the world (depending on the measurements). Both have made tremendous leaps culturally and politically.
"War is cruel, and you cannot refine it." William T. Sherman, a founding father of the theory on total war spoke those words (or something similar; depends on the source). Stalin said "The death of one man is a tragedy. The death of millions is a statistic." The Second World War was a conflict the likes of which we may never see again. Even today, its repercussions continue to echo. Allies and Axis alike, all those involved committed unspeakable cruelties in many forms. Against these, the atomic bombs pale in comparison. Like the America's involvement in the war, the atomic bombs don't count as a footnote simply because of the technological advances and work that went into them (by the way, the Germans were actually a lot farther away from a bomb of their own than we thought at the time). Total casualties from the bombings barely register with the wholesale slaughter of the war's largest battles.
The bombings of Hiroshima and Nagasaki were great tragedies. Calling them war crimes is a slippery slope at best. Bear in mind that all sides claimed strategic bombing to be abhorrent while engaging in it actively. The victors wrote most of the history books, and got to put their enemies on trial. Placed against the atrocities committed against civilians in the war, most for reasons having absolutely nothing to do with the military, the bombings were simply the final, climactic act to the greatest crime in human history.
P.S. Someone mentioned that the Japanese could have invaded the west coast of the U.S. Some sources I believe claim the Japanese might have gotten as far as Chicago. This is absurd. Completely absurd. The main Japanese army was still committed to conquering China, and an invasion force would have to be supplied by convoys that would take weeks to reach their destinations. Nothing of the sort was remotely possible.