The revolution always eats its own. That’s the lesson from a recent essay by Northwestern University’s Laura Kipnis.

Two students were so offended by her article in the Chronicle of Higher Education on why banning romantic relationships between faculty and students was silly that they filed a Title IX complaint against her.

Yes, that’s right, legislation that was originally supposed to combat sexual discrimination in public education and athletics is now being used to silence professors who write essays that contradict progressive wisdom.

The charges against Kipnis were dropped over the weekend, but not before she submitted to what she referred to as her “Title IX Inquisition.”

A law firm hired by Northwestern to investigate at first even refused to reveal the nature of the accusations against her. Lawyers told her they wanted to ask her questions but she wasn’t entitled to have her own lawyer present.

Nor could she record the session, during which she was interrogated about her writing, her teaching and even tweets she’d sent.

It’s hard to work up too much sympathy for Kipnis, though. One wonders where she’s been for the past two decades when kangaroo courts were set up at institutions of higher education all over the country.

Has she been rushing to defend all the men convicted by campus courts of sexual assault with no lawyers present?

Kipnis learned (much to her surprise) that, as she wrote, “any Title IX charge that’s filed has to be investigated, which effectively empowers anyone on campus to individually decide, and expand, what Title IX covers. Anyone with a grudge, a political agenda, or a desire for attention can quite easily leverage the system.”

No kidding. And Title IX is only the tip of the iceberg. Anyone with a political agenda and an ax to grind can get professors reprimanded, students kicked off campus and commencement speakers disinvited.

Did self-described feminist Kipnis rush to the defense of Ayaan Hirsi Ali or Condoleezza Rice when they were told they couldn’t come to Brandeis and Rutgers? (In an essay for Slate, Kipnis referred to Condi as President George W. Bush’s “Stepford Wife.”)

Has she been defending Christina Hoff Sommers when the students at Georgetown and Oberlin tried to prevent her from giving a visiting lecture and then demanding “safe spaces” to be protected from her harsh words?

Kipnis isn’t the only one who’s woken up to find the American university to be inhospitable to free speech. Take Janet Halley, a law professor at Harvard, who opposed Harvard’s new policies regarding sexual harassment and sexual assault.

Last week, she told the Crimson, “When I read the University policy last July, I said to one of my colleagues at the Law school . . . ‘You know we have to change the weather.’ ”

Now you want to change the weather? Where were you when the clouds were gathering in, say, the mid-’90s?

A decade ago, Halley wrote a book called “Split Decisions: How and Why To Take a Break From Feminism,” which suggested that feminism had become reliant on the state to police every form of bad male behavior and that this wasn’t necessarily a positive development.

But like so many academics, Halley didn’t have the courage of her convictions.

When asked by The Guardian about the witch hunt that got Harvard President Larry Summers forced out for suggesting that there may be biological reasons more men than women go into science, Halley offered this:

“Larry Summers lost his job. They brought down one of the most powerful men in the American academy. I think that the people who wield that feminist power should admit to it, and come to terms with the fact that they have it.”

And? Should he have been fired? The question is not whether feminists should continue to see women as victims when they clearly “wield that feminist power.”

The question is whether they should be able to wield that power to stifle academic freedom. But you didn’t see Halley rushing to the defense of Summers either.

Perhaps these women can work hard enough now to make up for the sins of their past, but it’s probably too little, too late.

Naomi Schaefer Riley is a senior fellow at the Independent Women’s Forum.