The bit that interests me the most is the inclination around 4:50 that the divide can be traced to "1987, when the Federal Communications Commission did away with the so-called 'Fairness Doctrine'."

I don't buy it. Imagine if that doctrine were in effect today. Every news channel would have to come up with a way to appease that rule. Who would be the arbiter?

When it was just the 3 main channels, they all pretty much went the same way.

If it's true that the amount of people viewing the main news channels create the divide, based on market share, the country would tilt much more toward the left. The only main channel that goes toward the right is Fox. The conglomerate that owns Fox isn't near as big as the next two biggest competitors. Media ownership wiki

I looked up the Fairness Doctrine It only requires that an opposing viewpoint be aired, not that it be given equal time. Under the Fairness Doctrine, I can imagine the networks reporting something like, everyone hates Trump. . . except his family.

When I watched it, I didn't focus so much on the fairness doctrine. But maybe this piece goes along with it. I focused on the part with the interview with Sean Hannity (that he is now mad about) that had Koppel saying that Hannity was bad for America because people like him have "attracted people who have determined that ideology is more important than facts."

One of the reasons I was less convinced about the fairness doctrine is because Koppel also interviewed the head of the NY Times. He thinks he's being fair. I don't agree. Would the FCC judge it differently? Probably.

This piece is even better where Hannity and Koppel agree that journalism is dead and that the opinion page of the paper as analogy for the news channels have become the front page.

When people are discarding facts in favor of ideology, that leads to people who are arguing based on emotions instead of facts, which leads to polarization. Magazine shows have taken the place of the news. Without facts in journalism on the major news channels, people don't have a fact based or logic based system to create their own ideology.