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.