I just finished reading one of many Sci Fi stories with a peculiar assumption that I've seen over the years. It is probably an outgrowth of the anti-war movement of the 60's and the anti-cold-war movement of the 70s and 80s --the idea is that when a civilization acquires nuclear weapons, that it is in danger of destroying itself, but that if it can somehow "evolve" through this stage without destroying itself, then the danger has passed.
My question is, why would the danger ever pass? Whatever form this "evolution" takes, whether a change in government, or social structure, or behavior, the authors never assume that it is an absolute change to pacifism. There are always continuing disputes and violence among humans. Therefore the change is only a matter of degree. But human technology will continue to improve and ever-more destructive weapons will become possible, even without military research. All it takes to make a planet-destroying attack is a good space tugboat that can grapple onto a big-enough space rock.
So as long as there is any friction, any violence, there will be the possibility of some maniac destroying the whole planet. How is the danger ever going to be over?
As I said, I suspect this thinking arises out of the peace movement. Some people were absolutely terrified of the prospect of nuclear war, and the Communist-supporting news media and entertainment media did all that they could to exacerbate this fear. For the Sci Fi authors writing back then, I think that this idea that there is a hump, and then once we are past the hump we will be safe, is a sort of fantasy wish fulfillment. It is the fantasy that one day the terror will go away.
For people writing since then, I suspect that they are looking at history, at how things turned out, and thinking that, "see, nothing happened and the Cold War is over." but they are not thinking critically. The Cold War is over because the US won. That might have not happened. And there is no reason to assume that such a standoff between great powers will never happen again --quite the opposite.