Ideas or memes buzz around like molecules in the air. If their average thermalized velocity exceeds gravitational escape velocity they gradually buzz away and no longer have any interaction with the Earth. Thats why hydrogen and helium are extremely common in the universe as a whole but there's not that much in our atmosphere. At least thats the astronomical analogy. If you atomize a culture and isolate and encourage subgroups to isolate and "other" each other, sort of divide and conqueror strategy on steroids, then you can end up with unconstrained groups that split into completely different cultures. Just like you take a population of one species, isolate two groups, and in evolutionary time (100K years?) you get two species that no longer care much about each other, might even eat each other. The Amish no longer have much if any common ground with the most extreme college SJWs. I'm not sure the SJWs have anything in common with the vast majority of the country, frankly. They've achieved escape velocity and will only wander further and further from the main culture and cluster of other cultures, like every other group thats achieved escape velocity from the main culture. Eventually interactions between people who are both foreigners in their own land will get really weird. Think of muslims with guns at FL nightclubs or with pressure cookers at marathons, my point isn't to be anti-muslim but to point out theres not much common ground anymore when the primary mode of interaction has declined to the level that it involves bloodshed. Once a group achieves cultural escape velocity, woosh, they're no longer part of the conversation, its us vs them yelling time at the best and kaboom bang bang time at worst.

Absolute power corrupts absolutely and its not hard to absolute power in the form of political consensus in legacy mass media, academia, hollywood, SV. And with that absolute power comes corruption. Telling the truth becomes an act of disbelief or apostasy, or you can faithfully believe while knowingly lie. Its not just the left, in that any group thats 99% composed of one political group tends to fester and get smelly, there's plenty of this on the right. You can only gain power by a public display of ever more devout true believer statements, truth is gone out the window. Ask yourself if people gain power in academia or the legacy media by telling the truth or by loudly proclaiming their devotion to the political causes that 99% of them share... that's what post-truth world means. A healthy balanced competition would force the truth to make an occasional appearance, but in a polarized consensus of groupthink its just a legacy fable. Remember when that stuff was about the truth? Yeah not so much anymore.

Combine the two ideas above and its a real mess. Atomized individuals and groups are broken off into groupthink hubs that rapidly share no common ground or affection with any other group and their interactions are based on gaining internal strength by showing their devout belief by denigrating the opposition. Traditionally this leads to revolution and civil war. I'd be surprised if the 50 states are together much longer. Frankly I can't wait, as the younger I am the better I'll come out in the rebuilding, assuming I survive. I'd rather rebuild at age 50 than age 70, for example.