Last month the novelist Lionel Shriver delivered the ultimate macroaggression at a writers conference in Brisbane, Australia: She spoke the truth. And it triggered a leftwing meltdown.

What did she say that caused the festival organizers to disavow her talk? She made the argument that fiction writers should be permitted to write fiction. Her speech—and events that have followed—shows how the secular religion of identity politics is threatening imagination itself.

“Taken to their logical conclusion,” Ms. Shriver said in her address, “ideologies recently come into vogue challenge our right to write fiction at all. Meanwhile, the kind of fiction we are ‘allowed’ to write is in danger of becoming so hedged, so circumscribed, so tippy-toe, that we’d indeed be better off not writing the anodyne drivel to begin with.”

To write in the voice, say, of a black woman if you are a white male writer, is rapidly becoming taboo—a form of cultural appropriation, to use the proper jargon. But such theft is the job of fiction writers. The novelist, as Ms. Shriver put it, is “the premier pickpocket of the arts.”

“If Dalton Trumbo had been scared off of describing being trapped in a body with no arms, legs, or face because he was not personally disabled—because he had not been through a World War I maiming himself and therefore had no right to ‘appropriate’ the isolation of a paraplegic—we wouldn’t have the haunting 1938 classic, ‘Johnny Got His Gun,’ ” she said.

Ms. Shriver delivered her speech while wearing a sombrero—a literal representation of her deeper point, which is that the job of fiction writers is to embody characters unlike themselves. If identity politics reaches its absurd conclusion, Ms. Shriver said, “all I could write about would be smart-alecky 59-year-old 5-foot-2-inch white women from North Carolina.”

If that seems like an exaggeration, consider the past few weeks in the life of Kendall Jenner, the supermodel scion of Kris and Caitlyn Jenner, who has come under fire for the sin of playing dress-up.

Ms. Jenner’s first transgression took place at New York Fashion Week in September, where, in Marc Jacobs’s show, she walked the runway wearing purple peep-toe platforms and a pile of woolen “dreadlocks” in various shades of pink, lavender and turquoise.

It wasn’t the babydoll dress that made the digital dictators lose their minds, but the dreadlocks—an apparently egregious act of cultural appropriation. Never mind that some of the models doing the appropriating were black. Or that the locks in question were completely fantastical, like an anime cartoon come to life. Or that the inspiration for the look was the signature hairstyle of the transgender filmmaker Lana Wachowski, one of the minds behind “The Matrix.”

Days later, Ms. Jenner had the gall to pose in pointe shoes for a Vogue España photoshoot. As one Twitter twit summed up the outrage: “The shoot was wrongfully appropriated. Dancers like Misty Copeland or Maddie Ziegler could have been way more powerful and graceful.”

In our surreal age, pretending is now politically incorrect. What’s the over-under on when Brad Pitt will only be permitted to play a celebrity going through a humiliating divorce? Give it a year.

Ms. Weiss is an associate book review editor at the Journal.