In 1987, philosopher Allan Bloom penned a brilliant indictment of the intellectual climate at American universities.

His best-selling book, The Closing of the American Mind, railed against the relativism and conformism of higher education institutions. He believed they had “failed democracy and impoverished the souls of today’s students”.

Thirty years later, universities in South Africa face a similar crisis. Captured by the dogma of decolonisation, many of the former ‘open’ universities are beginning to abandon the principles on which they were founded. These include open-minded inquiry, respect for individual rights, nonracialism and even – where clemency has been used to pardon criminality in violent student protests – the rule of law.

The consequence of decolonisation is a closing of the South African mind. On campuses, decolonisation has become an intolerant and authoritarian ideology that abhors dissent, ‘no-platforms’ people whose views its adherents do not share, and suffocates free speech.

This was well illustrated at the University of Cape Town recently, when the celebrated Kenyan writer Ngũgĩ wa Thiong'o delivered a public lecture. He was disrupted by students wanting to know why they should listen to him in a “hall built by colonialists”. They demanded that white audience members should leave the venue before he spoke.

This was extraordinarily shabby treatment for an African literary icon and someone who – as the author of a seminal text entitled Decolonising the Mind – would presumably have had something instructive to impart to his intellectual juniors.

But the fact is that many within the student decolonisation movement are bigoted, fanatical and utterly self-regarding. Their closed-mindedness manifests itself in puerile but dangerous calls to erase knowledge. Witness the Fallist student who claimed that science was “a product of western modernity” and insisted that “the whole thing should be scratched off”. In this totalitarian worldview, black is good and white is bad.

There is a debate to be had about decolonisation, even though South Africa’s colonial heritage is so deeply imprinted on its cultural and institutional landscape that one would have to embark on a scorched earth policy to “decolonise” in the proper sense of the word.

Of course, that is precisely what the student radicals want.

And, yet, as Achille Mmembe has argued, decolonisation is not about “closing the door to European or other traditions”. It is not about removing Shakespeare, for example, from the syllabus. Instead, it is about “defining clearly what the centre is”.

South Africa has not, formally at any rate, been a colony since 1910. The successive waves of decolonisation that swept through the rest of Africa between the 1950s and 1970s, broke – and were ridden – in a radically different historical context, globally and domestically.

As Jonathan Jansen recently wrote, there is a tendency nowadays to forget how “anachronistic” the language of the early post-colonial period is.

Among those who regard decolonisation as "the evil West and the rest of us”, there is also an “intellectual laziness” clothed in “political opportunism” that transposes “the rhetoric of anti-colonial struggle holus-bolus into contemporary society”.

Where such rhetoric is used to silence dissenting voices, the effect is to debase – and chill – public discourse.

Of course, because of our history of racial injustice, we live in a highly charged environment where – for better or worse, whatever your personal or political history – skin colour can determine how your utterances are received and interpreted.

Added to this, “decolonisation” is fast attaining the status of an idée reçue. Even university administrators now parrot the decolonisation mantra as if it were a moral imperative – a concept beyond reproach, a kind of public good.

The dogma of decolonisation has become almost hegemonic.

In this context, any speech act that does not explicitly condemn our colonial heritage in toto will inevitably be interpreted as a justification of colonization and colonialism – and, ultimately, racial oppression.

That is understandable even if it is myopic. Yet, it also highlights how brittle and fragile our public discourse has become, for, counter-intuitively, this is an accelerating rather than a decelerating trend.

There are three broader reasons why the domain of free speech has been so hollowed out.

Firstly, South African universities (and the wider liberal establishment) no longer prize freedom of expression in the way they used to. They have fallen prey to the creeping culture of conformism in speech and thought, censorship and self-censorship, and routinised offence-taking that is infecting university campuses worldwide.

As Mick Hume, author of the trenchant tract Trigger Warning has noted, far from being bastions of freedom, universities have “come to see themselves more as a womb-like fortress to protect young people from dangerous words and ideas”.

Concepts like “violence” have been so stripped and gutted of their meaning that anything anyone doesn’t like – across the spectrum of human expression, from works of literature and art to statues – can be branded as a form of “aesthetic” or “epistemic” violence.

Secondly, state censorship is resurgent. The Prevention and Combating of Hate Crimes and Hate Speech Bill is a prime example of that. Should the bill be enacted in anything like its current form, the South African mind will be well and truly closed for business.

Thirdly, online platforms like Twitter have attracted witch-hunting mobs that attempt to police people’s thoughts. They pursue, persecute and attempt to intimidate into silence those with whom they disagree. The impulse is profoundly censorious and punitive. Those who offend orthodoxy and disobey dogma must be punished and purged.

Even a once respectable commentator like Eusebius McKaiser, who used to have something worthwhile to say about the politics of race, has been reduced to playing the role of an outraged pantomime dame on Twitter, whipping up shock and horror in fewer than 140 characters. (“Is she a racist, everybody? Oh, yes she is!”)

The upshot of all of this is a closing of South African mind, as Helen Zille is experiencing to her detriment.