The Future: Does it change?

When asked by Billy how the Universe ends, a Tralfamadorian tells him that a Tralfamadorian blows it up by pressing a button that makes the whole world disappear, by accident. Of course, Billy wonders why that Tralfamadorian simply can't be prevented from pushing that button, but he is told that "He has always pressed it and he always will. We always let him and we always will let him. The moment is structured that way" (117). Each moment is structured specifically and cannot ever be changed because it simply has always been, is, and will always be that way. If this is so, there is no way to prevent destructive things such as war from happening in the future, unless the future is already structured that way.  Bad things that happen are accepted by Tralfamadorians because they know there is no way to change them. As for humans, we spend most of our lives trying to make sure bad things don't happen to us.
So what I'm wondering is, are our efforts for nothing? Do you believe that the future is ever-changing? That even the smallest of decisions can alter what happens to us and change the course of our lives? Or, do you believe what the Tralfamadorians say, that every moment has already been structured and the decisions we make are structured too, and therefore do not change the outcome of our lives?