Since its inception the term has been about adherence to party lines and enforcing ideological purity. The right wants to pretend they don't do it, so they want to attribute it to particular instances from the left, but they do the same thing all the time.

See the next paragraph on that same article you quote (Wikipedia, btw):

The phrase politically correct first appeared in the 1930s, when it was used to describe dogmatic adherence to ideology in totalitarian regimes, such as Nazi Germany and Soviet Russia.[5] Early usage of the term politically correct by leftists in the 1970s and 1980s was as self-critical satire;[8] usage was ironic, rather than a name for a serious political movement.[12][13][14] It was considered an in-joke among leftists used to satirise those who were too rigid in their adherence to political orthodoxy.[15] The modern pejorative usage of the term emerged from conservative criticism of the New Left in the late 20th century, with many describing it as a form of censorship.[16]