> How did we arrive to this point where a huge chunk of the population is in one reality and another huge chunk of the population is in another reality? Segregation of information sources? Politicization of media outlets? Self-reinforcing social bubbles? A combination of all of them and more?

No, that has nothing to do with it.

Take a look on wide base social polls across Western countries.

The seemingly "extreme" right turn in Europe at around the refugee crisis wasn't one unexpected if you count that.

It's just that huge social mass was very latent, and quiet as nobody wanted to be stigmatized as a nazi. Now, it isn't.

You cannot "deaf it out," and expect the problem to disappear.

Terrible social rifts can last centuries in silence. Example: Greek independence war was more than a century ago, and seemingly forgotten before it gave Ottomans the last blow, and then 50 years later, Turkey. And it seems it never really ended given what is going on in the Mediterranean now.

In the "peaceful" Western Europe, Schleswig war has ended 150 years ago, nations of Europe embraced in brotherly love, and the legacy of the conflict was ceremonially buried 10 times over, but people of Schleswig still tell of icy silence.