For those who follow the unfolding battle between cultural libertarianism and nannying authoritarians, it has been an interesting few weeks.

Late last month, a report from U.N. Women called on national governments to enforce censorship of the internet. It cited the worst research from the worst of the 1980s and 1990s conservative panics over obscene content in entertainment to make its case. One of the attendees, Anita Sarkeesian, sought to define comments like “You suck” and “You’re a liar” as “harassment.”

In the following week, activists tried to draw a link between a mass-murderer in Oregon and the anonymous imageboard 4chan. They argued that violence proved the need for more draconian moderation of websites, with appointed elites monitoring and censoring the content of ordinary posters.

This weekend, Breitbart senior editor Milo Yiannopoulos and Rebel Media broadcaster Lauren Southern were escorted out of a feminist “SlutWalk” by police officers. Their crime had been asking questions like “Do you believe in rape culture?” and “Should victims always be believed?”

Just a few weeks earlier, political commentator Steven Crowder was ejected from a similar event. Like Southern and Yiannopoulos, he had done little more than ask questions before he was asked to leave.

Meanwhile, in Canada, a man is on trial for criminal harassment after he disagreed with feminist activists. His tweets, the worst of which was “methinks the lady doth snark too much,” are alleged to have made the activists “fear for their safety.”

Left-wing identity politics has always had an authoritarian streak. Feminism in particular has betrayed a penchant for censorship since at least the 1980s. But that censorship was the product of a serious ideological debate, between the sex-positive and sex-negative wings of the movement.

This new censorship is different: it’s a panicky, desperate attempt to silence anyone who disagrees, and it doesn’t just come from feminism, but from the whole of the authoritarian Left. But why is it happening now?

The answer is simple: identity politics is in crisis. At the popular level, it is being rejected by an increasingly overwhelming majority of the population. Meanwhile, at the academic level, the old 1960s theories that long sustained left-wing radicalism are on their last legs.

Feminism is a useful example. Even among women, support for the ideology is at an all-time low. 82 per cent of U.S. women do not identify as feminist. Although it is still beloved by establishment media and political elites, the widespread public distaste for the ideology as it exists today is clear to see.

Popular uprisings such as GamerGate demonstrate the scale of public pushback against the worst elements of the movement, and comments from members of the public under any article by a mainstream feminist on the web are typically a mix of frustration, astonishment, and ridicule. Little wonder that “don’t read the comments” has become a feminist meme.

In the academy, the intellectual foundations of left-wing identity politics are being quietly but surely chipped away. For thirty years, the Left has based its world view on the idea that all inequalities are caused by social conditioning. According to this picture, “achievement gaps” between social groups, such as the gap between men and women in STEM fields, are caused by the social environment rather than natural inclinations.

This is why the modern footsoldiers of identity politics are so keen to tackle “micro-aggressions,” or subconscious bigotry. They really believe that casual remarks in everyday conversations are part of the root cause of inequality.

But the theory is long out of date. It is now ten years since Steven Pinker’s The Blank Slate blew apart the consensus on social conditioning. Pinker’s book was the crest of a rising tide of thinkers and cognitive scientists who believed that humans had evolved instincts and evolved differences, just like other animals, and were not mere products of their social surroundings.

The evidence has proven hard to refute. For example, studies of twins raised in adoptive households show that they remain almost identical, even when they are separated and raised in completely different environments. Studies of male and female babies show the beginnings of gender differences long before any social conditioning takes place.

As former New York Times science editor Nicholas Wade repeated on almost every page of A Troublesome Inheritance, which made the case for more research into racial differences, these facts do not imply an end to egalitarianism, just that the road forward is more complicated than previously thought. Of course, such caveats did not stop the inevitable accusations of racism.

When an old consensus loses its ability to win support and loses its ability to win arguments, its adherents have only one option: occupy the centre power at all costs, and use it to censor and intimidate the opposition.

That’s why feminists at the U.N. want to censor the internet, and why dissidents are being redefined as “harassers” and arrested. Supporters of radical identity politics can no longer win hearts and minds, so they have decided to do everything in their power to stop their opponents from doing the same.

It might seem impressive or intimidating, but the ability to call website moderators, the police, or even the U.N. against your opponents is not a sign of strength. It is a sign of decline and weakness. If the authoritarian Left had the ability to win arguments and persuade the public, they would not need to be invoke heavy-handed and illiberal authorities. As ever, censorship is merely the last weapon of discredited ideologies.

Follow Allum Bokhari @LibertarianBlue on Twitter.