This is about way more than onions. We are always in the danger of decline and regression to the dark ages. The world of rumors, beliefs, marketing and magical thinking is always there, biding its time.
It seems like Trump is a sign that what you fear is already happening. Look at the media his supporters consume. Listen to AM talk radio if you want to know how much the world is still controlled by "rumors, beliefs, marketing and magical thinking."
This is one of my greatest fears.
As one of my favorite examples of the very phenomenon you fear, just wait for the usual crowd of historical revisionists who will be along shortly to explain that the Dark Ages were really a time of widespread enlightened progress.