Japan has been an ally of the USA for a long time now.
On the other hand, every year they observe Hiroshima Day.
Moreover, Japanese people visit Yasukuni Shrine.
Then what is the catch?
The effects of Hiroshima and Nagasaki run quite deeply. One of the most profound effects is that Japan is very pacifistic and one of the few (if not the only country) that has outlawed war. Article 9 of the Japanese constitution prohibits the Japanese government from declaring war, although permits Japan to maintain a self-defense force. Since the end of WWII Japan's conditions of surrender and reliance on American markets has forced it to maintain US military bases which are widely disliked, especially in Okinawa where there have been numerous demonstrations against the American presence there (Blowback by Chalmers Johnson provides a very detailed analysis of Japanese concerns with US military presence).
Being the only country that had been the target of nuclear weapons, Japan also is very much against the development of nuclear weapons. One of the conditions of American forces being deployed in Japan is that nuclear weapons not be deployed on Japanese soil, and Japan has been stridently against weaponizing their nuclear program. Unfortunately, the American military establishment routinely mocks this requirement by having nuclear weapons deployed on naval craft stationed "in transit" in Japanese waters.
In essence, the relationship between Japan and America in the last 60 years has been complex. Japan's quick growth has been heavily reliant on preferential access to American markets and technology (to an extent where the US has been willing to harm its own balance of trade and allow Japanese firms to co-opt American companies trade secrets). In return the Japanese political establishment has allowed American forces to be stationed in Okinawa indefinitely. While this benefits most of Japan, Okinawa has had to surrender the best 20% of its land and has received the least of the benefits of Japan's growth. The Okinawans have thus been the most vocal opponents of the American military presence.
TO SUM: The benefits of America bending over backwards to provide favorable trading terms for Japan, and the ability of the Japanese to exploit this, has lead to a more prosperous Japan. These developments have generally overshadowed not only the past animosity over the war and nuclear bombings, but much of the tensions that arise between American militarism and Japanese pacifism as well. (The exception being in Okinawa of course).
While wating for a Japanese perspective here, here's an American's.
They do still seem to be a wee bit sore about the whole thing. I've noticed it appears to be a popular belief among the Japanese that the bombings were unnesscary. Whatever your opinion about this as a historical theory (a topic for another question, please), it does happen to be the position you'd need to take if you were in their shoes and wanted to be upset with the USA over it.
Note this goes both ways though. Our WWII generation is dying off now, but they've been the opinion setters for quite a while in this country. Being an ally with the same folks who slaughtered your brothers in Guadalcanal isn't easy.
At this point it seems to me the A-bombings are kind of like having a political difference with a cousin that you have to eat dinner with on holidays. We both know its there, but peace in the family is important, so both sides try very hard to avoid the topic.
It probably helps a lot that Japanese culture favors being very oblique about difficult topics, while USA culture is so blunt that such sublteties are generally lost on us. For example, ever seen a Japanese monster movie? You know the ones where some kind of nuclear thing (usually done by the USA) creates a gaint monster that destroys Japanese cities? Guess what those are really about. Its probably rather disturbing to the Japanese how much we in the USA enjoy them.
As the child of a man who was scheduled to be part of an invasion force of mainland Japan, and given the casualty estimates for that activity, it is likely in the extreme that I personally, and my children, as well as my sibs and their children, would not have existed if not for Hiroshima/Nagasaki.
From this standpoint, how can anyone reasonably condemn me for saying that I am thankful for the bombings?
Hiroshima and Nagasacki, terrible as they were, likely let my family exist.
Japan was the aggressor in WWII. This is a matter of record. Japan was further loathe to surrender in 1945.
Therefore, the moral burden for the bombings rests entirely on Japan.
I know that many Japanese are resentful of this perspective, though the perspective that the bombs were necessary and that that necessity was imposed by Japan is hard to argue with in any sort of rational way.
Could we be sure the Japanese would surrender without the awful hammer of the bomb?
Most historians think the answer to that question is "NO".
More to the point, most historians opine that the Japanese would have kept fighting if the Allies did not end the pacific war decisively.
So in the use the bomb side we have 1. Japan started the Pacific war with a sneak attack. 2. The Japanese had comported themselves as brutal fanatics throughout the Pacific war. 3. We could deal a knockout blow with the bombs, if we used the bombs before any other power developed or stole them.
On the don't use the bomb side we have: 1. They started the war, and if their military was not removed, would continue it. 2. It was the bomb, or an invasion, with aforementied devastating causualties for the Allies AND JAPAN.
Looks like the case for using the bomb was strong.
Remember,Japan was actively seeking their own bomb.
Thank God we got the bomb first.
Truman would have committed treason had he chosen not to use the bomb and invade.
The lesson of WWII Japan is that no country should ever allow a military dictatorship to take it over, even if you have to fight a civil war to stop it.
Military dictators may turn your country into an enemy of global peace (as Japan was in the early 1940s), In that case, the world is not to be blamed for whatever it has to do to put an end to your depridations.
The bomb assured that persons far more responsible than the allies (specifically, the military and political leadership of, as well as the populace of, the Asian Axis power, Japan) paid for starting the war in the Pacific, not third parties (Allied soldiers and their families).
No other outcome would be moral.
Yes, the A-bombs were terrible things.
May no human population ever feel treatened to the extremity of nuclear weapon use ever again.
More importantly, may no human population ever again be such a grave threat to world peace that the use of these terrible weapons seems necessary or rational.