Granted, there's always been an undercurrent of counter-culture in America. The Puritans had their witches. But by the 50's at least it was all buttoned up tight, and then exploded in the 60's and 70's, recoiled in the 80's, then everybody took a decade off in the 90's, and somehow in the 00's and 10's we all lost our fwcking minds.
The thing about mainstream American culture is that it pretty much had been under the thumb of mass media and religion. That's why the whole "fake news" attack is so devastating: our news has been fake. I read Noam Chomsky at an impressionable age and I recall the realization that we (in the USA) were living in what I called a "media blackout". Anything "they" didn't want you to know was simply omitted. It worked so much better than the Russian system.
But only until the Internet hit...
Every country with a heavily controlled media, with a people indoctrinated with a nationalistic fairy tale is having the same problems with the internet breaking down the old singular media narrative. The heavier the controls were, the larger the societal shock now.
It's ... touchy. We have all learned in the last couple years how to empathize with our American friends who just learned about Tucson or the MOVE bombing or something we learned in school that they just learned about from a superhero show or an apology. It's fine to blame it on your schools, it is definitely a bad move to mention the actual cause.
The reaction to a relatively tiny number of new acceptable ideas in the discourse has been pretty surprising, even to someone who thought they already had a low opinion of American culture.
And yeah, sure, the ad-generated enragement feeds don't help. But it is clearly mostly the small town kid getting exposed to more ideas thing, no question.