Northwestern University professor Laura Kipnis didn’t set out to become a martyr to free speech when she wrote a spirited essay in The Chronicle of Higher Education pushing back against “sexual paranoia” on college campuses.

To stir the pot, yes. To outrage the sensibilities of people she thinks are more naive than she is about sex, sure. But not make an example of herself in the fight against the stultifying regime of political correctness that grips academia.

This is the chilling fact at the center of the Kipnis affair: Her university investigated her for something she wrote, and not even something that was remotely anti-feminist or traditionalist.

No one will mistake Kipnis, who teaches filmmaking, for Phyllis Schlafly. Her books include “Ecstasy Unlimited: On Sex, Capital, Gender, and Aesthetics” and “The Female Thing: Dirt, Envy, Sex, Vulnerability.” In a starred review, Publisher’s Weekly said an evidently pro-adultery book she wrote combined “the slashing sexual contrarianism of Mailer” and “the scathing antidomestic wit of early Roseanne Barr” (sounds delightful).

This gets to the other fact that should be chilling for any liberal blasé about the Jacobin atmosphere of college campuses: If they can come after Kipnis, they can come after anyone.

Conservatives in academia have traded stories for years of fear on campus, of keeping their heads down and watching what they say lest they get harassed or fired. Now, the illiberalism of the left is being turned against its own. It is an illustration of the basic civil-libertarian point that any regime meant to stifle opponents eventually comes back to bite its architects.

The groves of academe have gone from what are supposed to be bastions of free speech to grim prosecutorial arenas where everything you say can and will be used against you. The potential McCarthyites sit in every lecture hall and seminar room and they are children of the left, students who have been trained and encouraged to be whiny, litigious and censorious.

This is a dystopia entirely of the left’s making. Its identity politics, feminism and hysteria about campus rape are ascendant on campus. On top of this, it is the Obama administration that weaponized Title IX in response to the alleged epidemic of campus rape and made it a clear and present danger to due process and freedom of expression.

In her essay, Kipnis argued that “in the post-Title IX landscape, sexual panic rules,” and the new campus codes are “a striking abridgment of everyone’s freedom” and “intellectually embarrassing.”

Kipnis should have known that her offenses were manifold. She called a he-said-she-said case of alleged unwanted groping at Northwestern, the occasion for a Title IX lawsuit, a “melodrama.” She questioned why women are called “survivors” instead of “accusers,” even when their accusations haven’t yet been validated. She professed mystification at the proliferation of students who say they find course material “triggering.”

Her critics could have argued back and hoped one day to be able to write as well as she does. Instead, they protested Kipnis (carrying mattresses, naturally) and reported her to the authorities.

In retrospect, Kipnis might as well have been a 13th-century monk taunting the Inquisition, or a 17th-century courtier of Charles I daring the Stuart king to throw him in front of the Star Chamber. She was duly accused of violating Title IX by writing an essay questioning the excesses of Title IX.

The university’s investigation of her was about what you would expect if Kafka’s Josef K. had caught the attention of the shadowy Committee of Affairs by writing an op-ed some people found uncongenial. It was difficult for Kipnis even to find out what she was accused of, which turned out to be violating a Title IX prohibition against retaliating against an accuser — even though all she did was write about a case that had nothing to do with her.

Kipnis was eventually cleared of the charges, but, as the cliche goes, the process was the punishment. Her subsequent essay on her experience, “My Title IX Inquisition,” has caused liberal soul-searching. It’s all fun and games when Condoleezza Rice gets disinvited, or when feminist-critic Christina Hoff Sommers protested, but when a film professor with high regard for Foucault is targeted, then clearly things have gotten out of hand.

The liberal explainer website Vox ran a piece a few months ago basically arguing that political correctness is a hoax perpetuated by oppressors. In the wake of the Kipnis piece, it featured a piece by a liberal professor saying he’s terrified of his liberal students, for the same reasons as Kipnis (tellingly, he wrote it under a pseudonym).

If liberals are really going to push back against the political correct regime on campus, they will have to do a number of things they will surely find unwelcome: tell students to grow up and realize that speech they disagree with is not tantamount to a physical threat; acknowledge that campus rape, even if it’s a serious issue, is not an out-of-control plague that requires dispensing with due process and other norms; and pressure the Obama administration to rescind its notorious April 2011 letter on Title IX that has roiled campuses and caught up innocent actors like Kipnis.

As it stands now, for a university not to take every Title IX accusation seriously is to risk a federal investigation and potentially a catastrophic loss of federal funding. So the normal bureaucratic impulse is to toss common sense out the window, and with it, protections for free speech.

In its statement on the Kipnis case, the campus free-speech group FIRE wrote, “The transmogrification of Title IX into an all-purpose excuse for knee-jerk overreactions to complaints about speech — sometimes only tangentially related to sex — is an unacceptable trend that endangers freedom of expression and undermines the purpose of higher education.”

Laura Kipnis just proved it.