That is only true in homogeneous cultures. A more realistic description of post-modern society is numerous pendulums swinging simultaneously, of different sizes and weights, impelled by different initiating forces.
I think it’s the lack of homogenization that drives the pendulum. The fact that there’s always some group of people who don’t like how it’s swinging making noise, blaming the world’s problems on it, drawing people to their thinking, eventually stacking enough people to make it start swinging the other way. Leaving behind people who like the other direction, lather rinse repeat.