> I think americans have the false belief that US is some of kind of benevolent force acting for the good of the world and promoting freedom and democracy.
A state can still make mistakes without saying it is good in everyway
The first and second event are undeniably different than the third in at least one crucial respect, the third was never even claimed to be unintentional by anyone involved - while the first two were repeatedly claimed to be unintentional by everyone involved. Of course, that doesn't prove they were unintentional but not even mentioning the accused's claims of innocence as you assert guilt does prove you're not presenting the comparison honestly.
> I think americans have the false belief that US is some of kind of benevolent force acting for the good of the world and promoting freedom and democracy.
I haven't thought that since I was a teenager, quite awhile ago. At certain points in history the U.S. did sometimes promote the cause of freedom and democracy but it was usually when doing so also aligned with U.S. strategic interests. A notable example was Radio Free Europe (aka Radio Liberty) started in 1950. The U.S. wisely realized the best counter to internal propaganda and totalitarian repression was just telling the truth, so RFERL was (almost always) genuinely unbiased, helpful for the cause of freedom AND good for U.S. strategic interests.
It's also worth mentioning that the Nagasaki bombing is often used as a case study on the ethics of war. They use it as a case study because, once I understood the full historical context of the war and what the U.S. side knew at the time, the decision to drop the A-bomb wasn't as clear-cut as I'd always thought. After spending four weeks on it in an advanced ethics class, my eventual assessment changed from absolute certainty to feeling the Hiroshima bomb was probably reasonably justified but that the Nagasaki bomb was not. The class started out 100% opposed to both but after four weeks was nearly evenly split on Nagasaki.
In the full context I'm kind of surprised there was any kind of split twixt the two given the full context that both H & N were on a very long target list being systematically worked through and both were destined to be destroyed and effectively levelled regardless of whether untrialled prototype nuclear weapons were tested on those cities or not.
As were 72 other cities (including Tokyo) prior to either H or N being touched.
ie. In the full ethical context the deeper question is really about programs of total war / total destruction rather than the edge case of using two targets as test sites for novel weapons.