"PC" is a term usually used disparagingly or ironically, but it refers to something real: an attempt to avoid hurting others. It emerged most likely from the Maoist concept of "firm and correct political orientation" and was adopted by the New Left, sometimes ironically, sometimes seriously—Toni Cade Bambara wrote in 1970 that "a man cannot be politically correct and a chauvinist too," calling out leftist men for their treading a party line that kept women trailing behind.
Political correctness led to multiculturalism. In my world, the world of children's textbooks, we found ourselves replacing Dick and Jane and Sally with Miguel and Shonda and Lian. Dad was no longer the only one who went to work, and Mom wasn't the only one who cooked. But guess what? Those edits reflected changes in the world; they did not create the changes.
The backlash, when it came, was furious. Allan Bloom started it with The Closing of the American Mind, which could have been a little-read grumpy philosophical tome but instead hit a nerve and became, as Camille Paglia later said, "the first shot in the culture wars." The 1990s were filled with anti-PC backlash, as exemplified by this article from the Times and the conference it describes.
"It's a manifestation of what some are calling liberal fascism," said Roger Kimball, the author of "Tenured Radicals," a critique of what he calls the politicization of the humanities. "Under the name of pluralism and freedom of speech, it is an attempt to enforce a narrow and ideologically motivated view of both the curriculum and what it means to be an educated person, a responsible citizen."
Rapidly the Right (Bloom, Kimball, D'Souza, Paglia, and others) redefined political correctness; and any positive implications PC might have had regarding inclusion, diversity, feminism, critical analysis, and tolerance were buried under the labels of dogmatism, favoritism (as in affirmative action policies), and, yes, a new intolerance. For a through-the-rabbit-hole view of this thought in action, see Chapter 4: "Freire and Political Correctness" in Peter Roberts's book on Paulo Freire.
Fast forward 20-plus years, and you have the GOP presidential candidate saying, "I think the big problem this country has is being politically correct. I've been challenged by so many people, and I don't frankly have time for total political correctness. And to be honest with you, this country doesn't have time either." And when you interview his followers and ask them what they like about him, 9 out of 10 mention that he says what's on his mind and isn't PC. By which they mean that he doesn't care if his words hurt others, if he's sexist or racist, or if he appears to be ignorant about the world. They like that about him because it's how they want to be. And they somehow believe that by pushing back on political correctness, they can correct the movement of the country toward a diversity they would rather ignore.
I recently called out a woman I know on FB who said of Hillary Clinton, "When it comes to schmoozing for campaign money, she ought to have a mattress strapped to her back with the meter running." I accused her of self-hating anti-feminism and said that I was a Bernie supporter, but people like her made me question my sanity. Whereupon she replied that she, too, was a feminist, but "To go easy on Hillary because of her gender would be sexist." And that is what anti-PC hath wrought: The inability to see how certain language applied to one gender/race/ethnicity/sexual orientation can be hurtful. Men would never be accused of "having a mattress strapped to their backs," not even in an anti-PC world. PC may be rigid and foolish and often hypocritical, but anti-PC returns us to the 1950s, a Stone Age world of Dick and Jane. That just isn't the world in which we live, no matter how much Trumpeters wish it were so.