It may be simpler than that: PC allows one to defeat opposing points, arguments and ideas without the bother of actually having to present counter arguments or facts, simply by dismissing or condemning the opponents themselves. It’s so much more difficult to address their actual statements and present convincing arguments against them. How much easier to simply dismiss the person, and their arguments vanish with them. PC is just a form of Ad Hominem.
An example of this is how the proponents of Anthropogenic Global Warming never, ever address the contrary facts and observations of their skeptics, but by dismissing them as “deniers” in the pay of oil companies, those facts and observations never have to be explained.