> Why would you assume that the full spectrum of opinions on an issue would be unchanging?
The spectrum of actual opinions (which is related to the Overton window) may not be unchanging, but the spectrum of all possible opinions by definition can't change. The range of opinions on nuclear weapons goes from "Let's use all of the nukes that exist right now, and also build more and use those, at any cost." to "Nuclear weapons are so evil that any amount of sacrifice is justifiable if it effects even a minuscule change in the likelihood of nuclear weapons being used, or more being built, or existing ones dismantled." This has been true since they were invented, and will continue to be true forever. But both opinions are outside the Overton window, which changes over time.
The spectrum of actual opinions (which is related to the Overton window) may not be unchanging, but the spectrum of all possible opinions by definition can't change. The range of opinions on nuclear weapons goes from "Let's use all of the nukes that exist right now, and also build more and use those, at any cost." to "Nuclear weapons are so evil that any amount of sacrifice is justifiable if it effects even a minuscule change in the likelihood of nuclear weapons being used, or more being built, or existing ones dismantled." This has been true since they were invented, and will continue to be true forever. But both opinions are outside the Overton window, which changes over time.