Well, okay, one example of PC culture is sensitivity towards microaggressions. Based on your previous comment, you're probably already rolling your eyes, but bear with me. Microaggressions are usually (and very broadly) defined as actions which unintentionally marginalize people. These actions are almost never noticed by the person at fault -- that's what makes them "micro." Examples include things like calling a black colleague "aggressive" when they're arguing -- that particular language has been applied to black people for a long, long time to cast them as violent or criminal, and thus comes across differently than when applied to a white person.
Anyway, I list that as an example because what you're talking about isn't actually an example of political correctness (which is, again, a shitty term for basic respect and awareness of social context). Humans like black-and-white issues. It's really nice for us to be able to put things in boxes. So when we perceive someone's action in a certain way, our gut instinct is to cast that entire person as that way. Do people sometimes take someone's rudeness (even if accidental) and brand them a racist, discarding all of their opinions? Absolutely. Do some of my family members hear that I voted for Hillary and decide that none of my opinions have value? Also certainly. Humans are dogmatic. "Political correctness" is an umbrella term for cultural sensitivity, and can (like any idea) be applied dogmatically. It is not fundamentally dogmatic.
Anyway, I list that as an example because what you're talking about isn't actually an example of political correctness (which is, again, a shitty term for basic respect and awareness of social context). Humans like black-and-white issues. It's really nice for us to be able to put things in boxes. So when we perceive someone's action in a certain way, our gut instinct is to cast that entire person as that way. Do people sometimes take someone's rudeness (even if accidental) and brand them a racist, discarding all of their opinions? Absolutely. Do some of my family members hear that I voted for Hillary and decide that none of my opinions have value? Also certainly. Humans are dogmatic. "Political correctness" is an umbrella term for cultural sensitivity, and can (like any idea) be applied dogmatically. It is not fundamentally dogmatic.