This is the dumbest thing I have seen come from Jonathan Haidt. If social media is this powerful a destabilizer of societies, I wonder how Haidt explains first world countries like Germany, Canada, and most of the rest of the planet that have social media but haven't fallen into the same sort of divisiveness the US has.
They're more homogeneous in almost every way, including wealth, race, culture. They're also smaller.
It's a popular trope thrown mostly around by Americans, and is sometimes (often) a dog whistle for racism.