Whatever happened to ‘Never Forget’?

When I was growing up, the dark miasma of the Holocaust was still so pervasive that the famous slogan “Never Forget!” seemed almost irrelevant. How could anyone forget Hitler and his murderous goose-steppers? It was hard to imagine a world where that supreme evil was not remembered as a stern and awful warning. I heard Holocaust survivors insisting that we must never forget, and I thought they were just repeating the obvious. Why did they have to keep on saying it?