Midway through my opening address for the Brisbane Writers Festival earlier this month, Yassmin Abdel-Magied, a Sudanese-born Australian engineer and 25-year-old memoirist, walked out. Her indignant comments about the event might have sunk into obscurity, along with my speech, had they not been republished by The Guardian. Twenty minutes in, this audience member apparently turned to her mother: “ ‘Mama, I can’t sit here,’ I said, the corners of my mouth dragging downwards. ‘I cannot legitimize this.’ ” She continued: “The faces around me blurred. As my heels thudded against the grey plastic of the flooring, harmonizing with the beat of the adrenaline pumping through my veins, my mind was blank save for one question. ‘How is this happening?’ ”

I’m asking the same thing.

Briefly, my address maintained that fiction writers should be allowed to write fiction — thus should not let concerns about “cultural appropriation” constrain our creation of characters from different backgrounds than our own. I defended fiction as a vital vehicle for empathy. If we have permission to write only about our own personal experience, there is no fiction, but only memoir. Honestly, my thesis seemed so self-evident that I’d worried the speech would be bland.

Nope — not in the topsy-turvy universe of identity politics. The festival immediately disavowed the address, though the organizers had approved the thrust of the talk in advance. A “Right of Reply” session was hastily organized. When, days later, The Guardian ran the speech, social media went ballistic. Mainstream articles followed suit. I plan on printing out The New Republic’s “Lionel Shriver Shouldn’t Write About Minorities” and taping it above my desk as a chiding reminder.

Viewing the world and the self through the prism of advantaged and disadvantaged groups, the identity-politics movement — in which behavior like huffing out of speeches and stirring up online mobs is par for the course — is an assertion of generational power. Among millennials and those coming of age behind them, the race is on to see who can be more righteous and aggrieved — who can replace the boring old civil rights generation with a spikier brand.

When I was growing up in the ’60s and early ’70s, conservatives were the enforcers of conformity. It was the right that was suspicious, sniffing out Communists and scrutinizing public figures for signs of sedition.

Now the role of oppressor has passed to the left. In Australia, where I spoke, Section 18C of the Racial Discrimination Act makes it unlawful to do or say anything likely to “offend, insult, humiliate or intimidate,” providing alarming latitude in the restriction of free speech. It is Australia’s conservatives arguing for the amendment of this law.

As a lifelong Democratic voter, I’m dismayed by the radical left’s ever-growing list of dos and don’ts — by its impulse to control, to instill self-censorship as well as to promote real censorship, and to deploy sensitivity as an excuse to be brutally insensitive to any perceived enemy. There are many people who see these frenzies about cultural appropriation, trigger warnings, micro-aggressions and safe spaces as overtly crazy. The shrill tyranny of the left helps to push them toward Donald Trump.

Ironically, only fellow liberals will be cowed by terror of being branded a racist (a pejorative lobbed at me in recent days — one that, however groundless, tends to stick). But there’s still such a thing as a real bigot, and a real misogynist. In obsessing over micro-aggressions like the sin of uttering the commonplace Americanism “you guys” to mean “you all,” activists persecute fellow travelers who already care about equal rights.

Moreover, people who would hamper free speech always assume that they’re designing a world in which only their enemies will have to shut up. But free speech is fragile. Left-wing activists are just as dependent on permission to speak their minds as their detractors.

In an era of weaponized sensitivity, participation in public discourse is growing so perilous, so fraught with the danger of being caught out for using the wrong word or failing to uphold the latest orthodoxy in relation to disability, sexual orientation, economic class, race or ethnicity, that many are apt to bow out. Perhaps intimidating their elders into silence is the intention of the identity-politics cabal — and maybe my generation should retreat to our living rooms and let the young people tear one another apart over who seemed to imply that Asians are good at math.

But do we really want every intellectual conversation to be scrupulously cleansed of any whiff of controversy? Will people, so worried about inadvertently giving offense, avoid those with different backgrounds altogether? Is that the kind of fiction we want — in which the novels of white writers all depict John Cheever’s homogeneous Connecticut suburbs of the 1950s, while the real world outside their covers becomes ever more diverse?

Ms. Abdel-Magied got the question right: How is this happening? How did the left in the West come to embrace restriction, censorship and the imposition of an orthodoxy at least as tyrannical as the anti-Communist, pro-Christian conformism I grew up with? Liberals have ominously relabeled themselves “progressives,” forsaking a noun that had its roots in “liber,” meaning free. To progress is merely to go forward, and you can go forward into a pit.

Protecting freedom of speech involves protecting the voices of people with whom you may violently disagree. In my youth, liberals would defend the right of neo-Nazis to march down Main Street. I cannot imagine anyone on the left making that case today.