Having read that entire article in the OP, which was essentially a long, bitter rant about the spread of ideas other than white Anglo-Saxon Christian views, the last time I can remember encountering such a creative interpretation of history, aimed at the marginalisation of others and wrapped in a disguise of faux-academia was when I watched sections of The Eternal Jew, the Goebbels-approved Nazi propaganda film that told the "story" of how Jews had supposedly spread through Europe and stolen from other cultures.
"Political correctness" is a loaded phrase, it brings to mind officious censors being overly sensitive about anything that's said about anyone from a non-white, non-straight, non-Christian background. That saying you can't say this, or that about other cultures is simply a jobsworth with too much time on their hands getting involved where they shouldn't. Sometimes, this is true.
On many other occasions however, prevention of harassment of groups or individuals on the basis of race, religion, sexual orientation or any other irrelevant factor that does nothing to determine a person's worth is a critical struggle. We don't live in a world where white, straight and Christian is the "norm" anymore, and nor should we, and nor should humanity ever have. There is no "cultural Marxist" conspiracy, it's just the latest brainwave of religious conservatives bitter at the fact that they no longer call the shots. Humanity has moved on.