You can get into a more general argument about what kinds of acts are tolerated in war, but the atomic bombs don't seem to stand out either way. The real question is, is it acceptable to target a civilian population? What about even if doing so will ultimately save more lives? Look at the civilian death toll Japan had been inflicting on China, for instance; is it ethical to inflict a smaller number of Japanese civilian deaths in order to prevent a larger number of ongoing Chinese civilian deaths?
Terms that were un-necessary. Japan still has an emperor no? Could have ended the war much earlier if they wanted to.
And another factor is that we haven't had a nuclear war since Japan, which showed the horrors of nuclear warfare. Had that not happened, maybe real nuclear weapons would have been used by someone later on, when they were much more powerful and more numerous, and even when both sides possessed them? The bombings have helped ensure that something much worse hasn't happened since.
And you know what, the Japanese government deserved it. They started the war, killed millions of people in the process (including many millions of civilians in Asia), and then had the gall to try to bargain for decent surrender terms after all that horror they caused? Nope. Sometimes harsh punishment is necessary.
The government yes. The people did not elect them. They had no choice in the matter, and were also trained into full propaganda mode many years before the war. So targeting civilians with fire-bombing is certainly questionable. Even McNamara said that what they did in Japan would be considered "crimes of war" in case they did not end up victorious.
No matter which way a leader comes to power, the population pays the taxes and the ultimate tolls.
This means that when we are on the inside, in the country, we can't be more or less complacent with a bad dictator than a bad elected leader, we always pay the price for what they do. It's always our problem.
The offer was a negotiated surrender that would end hostilities with some face-saving concessions - specifically for the Emperor.
There isn't a perfect historic record of the negotiations, but it's clear the Allies pushed hard for unconditional surrender.
If the argument is about minimising the loss of lives, the war could have been ended much earlier.
If the argument is about the post-war relationship between the allies/survivors, and which actors the bombs were supposed to send a message to, the situation is much more complex.
The Japanese leaders didn't deserve them after what they'd did, and it really would have changed the entire post-war dynamic between Japan and other countries, and even more importantly, between the Japanese government and its own people.
Here's one term from the Potsdam Declaration, which the Japanese rejected: "The Japanese Government shall remove all obstacles to the revival and strengthening of democratic tendencies among the Japanese people. Freedom of speech, of religion, and of thought, as well as respect for the fundamental human rights shall be established."
It's not unreasonable to say that had the Allies not continued prosecuting the war and pushing for unconditional surrender that Japan might not have ended up with a democratic government at all. It would have been much worse if the emperor and military figures had stayed in charge, and could have easily led to more repeats of wars of Japanese imperialism.
So yeah, I think it's important to look at it holistically and see what the actual long-term outcome after the war was (which was about as ideal as was possible), vs. what would've happened had we just ended the war as quickly as possible to minimize casualties but without getting wholesale reforms in the Japanese form of government.
Applying that standard, there would not be a single American left alive for the constant war they wage since the end of WW2.
In warfare more than almost anything else, might matters.
I know we've done some shitty things to a variety of different countries over the years, but those acts are never going to be reciprocated in kind because they're the kinds of acts that only the powerful can do to the weak, and the US is not weak. It's not a value or moral judgment, it's just the reality of how power and force work.
Wonder what you have to say about what the US deserves after the Iraq war?
Japan was plenty concerned, especially remembering the last time they met USSR military. [2]
In fact, memories of that smashing were arguably the reason Japan turned east to Pearl Harbour, rather than west to Soviet Union. [3]
[1] https://www.warhistoryonline.com/instant-articles/red-army-i...
[2] https://en.wikipedia.org/wiki/Battles_of_Khalkhin_Gol
[3] https://www.goodreads.com/book/show/13102802-nomonhan-1939
What Zhukov had shown at Khalkhin Gol, just as against Germans, was that with a significant advantage in manpower and equipment (double the manpower, 7 times the tanks) Soviets can actually beat up someone.
After WW2 it was more convenient for everyone to say that Hiroshima was what ended the war. The picture of a bunch of crazy generals in a bunker planning Japanese resistance until literally the last man woman and child is not very flattering.