Strategikon has a great video up on the origins of political correctness and the New Left in the Frankfurt School.
The New Left’s cultural critique of capitalism has been a fabulous success compared to the Old Left’s economic emphasis. Marxist economics was demolished by the Austrian economists and Marxist politics was ruined by its own bloody history of totalitarianism. But the New Left is now our cultural ideal and is indoctrinated into children in government schools. It has infiltrated every aspect of our culture to the point that it is hard to see because there is nothing else to distinguish it from.
The New Left was able to evolve so easily from the Old Left because they shared the same goal: the destruction of capitalism. It should be remembered that the first faction to fight for that goal was the religious conservatives. Marx secularized their arguments against capitalism. A big story in the coming decades could be the rapprochement of the New Left and the religious conservatives as they find common ground in their struggle against selfish, worldly capitalism.