"People who object to the bombs on Hiroshima and Nagosaki should read this article. "
The atrocities of the Japanese were well known in US intelligence circles and there is no doubt that it affected the scale of violence that the US thought appropriate.
In many histories I have read, the mentality by the end of the war was that "we fought Germans, but we kill Japanese."
Before I get set upon by the FR hordes, let me say that I don't think that was unreasonable given the steady ramp-up of brutality throughout the war, and that ramp-up was initiated by the Axis. They sowed the wind and reaped the whirlwind.
It was fairly well-known, as the war progressed, that Allied POW's were brutally mistreated by the Japanese. Japanese troops were also well-known for fake surrenders, where they would pretend to surrender, and then try to bushwhack the GI's who went to accept the surrender. As far as I'm concerned, the Japanese got less than they deserved (in terms of war casualties). At the same time, there's no comparison between the genocidal policies of the Nazis*, and the classic imperialistic bent of the Japanese.
* Where if being of the wrong ethnicity was fatal to you and your family, in spite of dedicated government or military service.
Tokyo and Kyoto were both in range of American planes--if the United States was seeking the most deaths, and the largest societal impact, those two cities could have been hit instead of the two which were.
I once read that about 1/3 of American POWs died in Japanese captivity, while only about 3% captured by the Germans did. As shown by this article, the Japs had no regard at all for international agreements like the Geneva Convention. I have to wonder if there isn't some correlation with the fact that Japan has been more resistant to the spread of Christianity than almost any other country outside the Islamic world. Christianity still had some hold over many individual Germans.
There were atrocities by Americans against Japanese as well. Charles Lindbergh traveled extensively in the South Pacific during the war, and recorded atrocities in his "Wartime Journals". He recorded instances of body part collecting. Gold teeth collecting, and other barbarities against the dead. He also recorded the fact that there were virtually zero Japanese prisoners. The story has been perpetuated since the war that the Japanese "fought to the death", prefering to die in battle rather than be captured. Lindbergh says that American soldiers did not allow surrender. We killed them all. Lindbergh told of an order from a commander to give day passes to soldiers who brought in live Japanese prisoners, because they needed prisoners for intellegence gathering. They were suddenly swamped with prisoners. But as soon as they stopped giving out day passes for live prisoners, there were no more prisoners.
Granted, this is not as barbaric as what the Japanese did. It was a brutal war, and Americans returned at least some of the barbarity shown us. Except for Lindbergh, this story is virtually unknown.