Without picking quotes, I firmly believed that nuclear deterrence of the 1950a and 60s was no more than the threat of wreaking similar levels of damage as 'terror' bombing of the 1940s. I use the word 'terror' advisedly.
Deterrent policy was evolved by politicians that had served through the 1940s and controlled by military commanders similarly experienced in such devastating weapons effects.
Now, nearly 70 years later, I can look back and see that such devastating attacks against a whole population is morally wrong as we now have the luxury of accurate targeting against a political and military leadership. From that viewpoint I cannot see the value of a nuclear deterrent as it would cause immense collateral damage against what is essentially an innocent civil population especially women and children.
While we would argue that our deterrence is aimed at an enemy leadership we credit them with a similar fear of destruction of civilians as we ourselves fear. As it is possible that they answer to god and not the people I fear that nuclear deterrence is now invalid.
Had World War 2 started in Europe 4-5 years ago, would we still feel the need to destroy enemy cities? To do so in retaliation would indeed be a crime against humanity but retaliation was exactly what we planned in the 60s and the world was not wholly different from the 1940s.
In the 40s it was a totally different world from the 21st Century and it is difficult if not impossible now to attribute guilt for actions then.