In communism, political incorrectness might get you shot, but far more likely might be taken into account when you next sought a holiday or promotion. For the most part, the enforcement of political correctness under communism was every bit as decentralized as the enforcement in the US.

Similarly with thirteenth century punishment for heresy, the main punishment being that one was unlikely to receive tenure. No one respectable got tortured or burned at the stake, though Roger Bacon got solitary confinement on bread and water.

And the enforcement in the US is ultimately highly centralized. The reason your boss will fire you for wrongthink is that when his business gets charged with racism, all his employees will be scrutinized for wrongthink. Most discrimination charges do not involve an employer calling a member of a protected group a derogatory name, but rather an employee revealing unapproved views unaware that there are spies present who will rat on him. A member of a protected group heard of the unapproved views - in some cases he would had to have been listening at keyholes to have discovered the unapproved views and have his feelings hurt, and I suspect that in fact these unapproved views were only discovered during the disclosure phase, and the complainant could hypothetically have heard them at the keyhole, rather than actually heard them.

For the most part, enforcement of political correctness under communism worked in exactly the same way as in the US - through employment and academic admissions.