Feminist old guard: “Women Against Pornography” march on  Times Square, New York, in 1979 (image: Barbara Alper/Getty Images)

For years a few of us have warned that modern “liberals” would live to regret abandoning the principle that you should only censor speech when it incited violence. We would enjoy our vindication if the unravelling of progressive assumptions was not so extraordinarily menacing.

Political correctness is eating itself. It is abandoning its children, and declaring them illegitimate. It is shouting down activists who once subscribed to its doctrines and turning its guns on its own. Women are suffering the most, as they always do. “Radical feminist” is now an insult on many campuses. Fall into that pariah category, and your opponents will ban you if they can and scream you down if they cannot.

It is tempting to say “serves you right” or “I told you so” to the feminists on the receiving end of the new intolerance. But you will not understand how Western societies have become so tongue-tied and hypocritical unless you understand the human desires behind the feminists’ original urge to suppress, which now lie behind their enemies’ desire to suppress them.

A generation ago, a faction within Western feminism campaigned to ban pornography. They believed it caused harm by inciting men to rape, but couldn’t prove it. Despite decades of research, no one has been able to show that pornography brutalises otherwise peaceful men. So they added the argument that sexual fantasy should be banned because it spread harmful stereotypes that polluted society. Unfortunately, for them, they could not substantiate that claim beyond reasonable doubt either.

“You have no identity, no personality, you are a collection of appealing body parts,” the American law professor Catharine MacKinnon told her followers in the 1980s. Pornography ensured women were assessed only by their looks. It “strips women of credibility, from our accounts of sexual assault to our everyday reality of sexual subordination. We are reduced and devalidated and silenced.”

For all its faults, America has the First Amendment, which protects free speech and freedom of the press. The US Supreme Court duly struck down an ordinance MacKinnon and Andrea Dworkin drafted for Indianapolis City Council in 1984 which would have allowed women who could say they were harmed by pornography to sue. It might have killed the law but it did not kill the movement. The impulse behind the original demands drives campaigns against sexist advertising and naked women in tabloids to this day.

Even if you think, as I do, that a wing of feminism degenerated into a puritanism not too far away from the God-given puritanism of the Christian Right, you should accept that debates about free speech are unavoidably ferocious because the urge to suppress is not some feminist peculiarity but a near universal desire.

When he drafted his “harm principle”, which placed liberal limits on speech, John Stuart Mill considered the case of corn merchants. They were the bankers of the mid-19th century, hated and feared by the poor. Radical agitators denounced them for hoarding grain and forcing the masses to choose between inflated prices and starvation. Conservatives feared riot and revolution, and wanted to protect the social order by silencing the agitators. Mill said they could censor only if radicals were inciting a mob to commit a crime: to burn down a corn merchant’s house, or attack him in the street. Incitements aside, radical journalists should be free to write and say what they wanted. Their opponents could test their ideas, and mock, expose and refute them. They could use all the weapons a free society offered to change the public’s mind, but they could not use the law to asphyxiate debate, because in the silence that followed a dreadful conformism would set in.