PC seems, to my eyes at least, seems most entrenched in what could be best described as the Protestant countries of Europe, and it's my belief that that the two are more than just casually linked.
It's my belief that that Protestant culture effectively puts into place conditions which allow PC to thrive.
As a Catholic, I have doctrinal differences with the Protestant religion, but perhaps Protestantism's most malign error lays not in its doctrine but in its understanding of man, namely in his capacity to think. It's what Paul Gottfried described as the "rationalist fallacy". The belief that everyman is a profound and clear thinker, able to objectively look at the facts without bias; It's the myth of the rational everyman.
The truth is that men are rational when things are simple to grasp, immediate and concrete in concept, but as the subject matter become more remote, abstract and non-pressing so does the capacity of men to rationalise well about them. In this regard, religion is more likely to be prone to intellectual errors simply due to its subject matter than the house plumbing.
Religions can be though of being both pure and applied, in that the real world application of the religion may sometimes be at odds with the divine message. The average man's conception and practice of religion may be at odds with the theology, simply because he does not understand or is incapable to bringing together separate strands of thought.
For example, Protestant critics of Catholicism frequently lay the charge the Catholicism is a form of crypto-paganism with Catholics worshiping other deities beside God. They, of course, base this charge on their observations of Catholics and their relation with saints, relics, and the Mother of God. "Pure" Catholic theology recognises that the only proper object of worship is God, however as a Catholic, I can understand the Protestant claims because many of the faithful behave in manner that justify them. Simple men, trying to grasp the complexities of Catholic thought, corrupt it into neo-pagan forms. They carry crucifixes for good luck, and celebrate, rather too fervently for my liking, saints and relics. This subject deserves several posts on its own, but suffice when Catholicism becomes corrupted it assumes a pagan flavour.
Just as Catholicism, in corruption, assumes a certain flavour, so does Protestantism. When a Catholic goes theologically bad, he goes pagan and become superstitious, when a Protestant goes bad, he becomes utilitarian and "ethical". It's not Protestantism per se which fosters political correctness but its practical corruption by the common folk.
In theory, the Protestant has a personal relationship with God, a good and reflective religious life, and free of Papal Authority, the Protestant is free to read the bible and apply it to his life. The assumption being that the average Protestant can do this objectively, logically and without bias. And it is true that amongst rigorous and honest thinkers, this can produce quite holy men, the problem is though that rigorous thinking is always exceptional in any society and in the end what happens is that average Protestant behaves like the average catholic, he pretends that he thinks and muddles things up.
The Rationalisation Hamster whilst nearly supreme in women also operates to a degree in men and the end result of its operation is contingent upon the cultural milieu in which it operates. In a religion that allows you to self-interpret the bible, strong willed men and women of shallow thought and objectivity will frequently find that their interpretation aligns with their feelings (Quelle surprise!); The end result is social sanctified practical utilitarianism. Once again this not Protestantism as it is meant to be, but its corruption by the average thinker.
This effect was mitigated somewhat whilst church attendance was practiced. The preacher, usually with some theological training, could sway the most shallow thinkers and prevent the most stupid errors by providing a convincing argument, but as church attendance has faded, the average man has been left with his own thoughts. The ship is adrift.
Religion is the basis of a society's culture and in a Protestant culture without a defacto central authority, morality becomes aligned with feelings. The Good God becomes the fluffy-bunny God in rudderless protestant cultures, because in the end, the human rationalisation hamster ensures that morality aligns with desired feelings. (Some people enjoy being miserable. Is Puritanism the inevitable product of miserable religious people in Protestant culture?) The religion goes "soft" and it's in this cultural milieu that PC establishes its roots.
However it would be a mistake to assume that a Protestant cultural environment causes political correctness. It doesn't. For PC to really establish itself something else is needed.
The second factor that needs to be considered is the societal cognitive process. i.e how a society as a group thinks. Now it needs to be understood that very few people, in any society, are independent thinkers, most people think along the lines that they have been taught. Here the pernicious effect of cultural Marxism rears its ugly head. The entrenchment of Marxist thought in our universities means that the products of that system--our future governing/managerial class--think along Marxist lines. This does not mean that the products of our universities are explicitly Marxist, rather the graduates tend to interpret life through the Marxist perspective In effect, what the universities ensure is that graduates end up with a de facto Marixist rationalisation hamster.
A digression. The Left is far more represented by graduates of the arts and the social sciences than by the STEM majors. Why? In my opinion, it's the strict empiricism of the STEM courses that provide a de facto inoculation against structuralist thinking; it's very hard to find oppression in chemistry or physics. Thinking along stucturalist lines in these disciplines results in failure.
PC can then be thought of a fusion product, resulting from the convergence of abuse of Protestant Christianity into "Christian-fluffy-bunny" utilitarianism and Marxist cognitive interpretation.