Your last paragraph makes a terrible moral argument: Yeah, maybe I am waging a war today, but's in the interest of the future peace!
I don't think your hypothetical assumption that 20th century peace could not be made without using nukes in WW2 is valid.
Why not even turn it up and say that future peace from nuclear weapons is impossible without living through the global thermonuclear war? Clearly, most people can imagine dangers of that, so they are perfectly capable of imagining dangers of only 2 nukes being used, without them actually being used.
I wasn't trying to make a moral argument.
With the information available at the time, dropping the nukes was immoral, and unjustifiable. The public justifications and the ones accepted by the standard western historical narrative do not hold up to scrutiny.
Despite that, I'm claiming that the decision probably inadvertently saved lives.
But that's not a moral argument. There were other means to save lives from nuclear apocalypse, and the US is complicit in its own actions that they've done to ensure a cold war with the Soviet Union.