Suppose that in July 1944 I were in a position to assassinate Hitler, and suppose also that I knew then what is generally known today about the Holocaust. If I did not try to assassinate Adolf Hitler in that circumstance, it would more likely be due to fear for myself or for my family than to moral scruples about whether the act was justified.
Yes, I might be in the same boat. But it is the knowing "what is generally known today about the Holocaust" that is the kicker. I mean, considering circumstances, time, etc. I don't think it is unfair to say that there were a huge amount of available non-violent options, and I sincerely think that it would have halted further, greater violence and atrocity. But we have to know that, and know what is going on, before we can ultimately morally make that decision. I think there was probably sufficient knowledge at the time to make this decision, and any further knowledge just cements it.
Of course, this is all based upon the idea that less suffering/death/violence is 'better' than more, but that's an even more abstract conversation for another thread.
Rather, my point is that if a stable, democratic and accountable government will act in this way, then there is almost certainly no government which won't.
I think you will call me naive, but I think perhaps this will not happen again. I'm not claiming there will never be another nuclear strike, but I think the mindset for strike number three will be quite different, if it happens. The world (or rather, the people in governing roles in nation-states) hasn't necessarily "grown up", but it has changed, and it does take into account the reactions to things that happened in the past.