Back when she was a sassy feminist, complete with 1970s shag hair and a repartee in man-bashing one-liners, I bet Germaine Greer never imagined she’d one day get into trouble for saying that truck drivers with penises are not women.

And yet it’s happened. On Q&A, Greer, who in the past had to say ‘men hate women’ or praise Mao Tse-tung in order to get starched observers choking on their chiantis, caused outrage by saying: ‘If you’re a 50-year-old truck driver who’s had four children with a wife and you’ve decided the whole time you’ve been a woman, I think you’re probably wrong.’ I hope next time she’s on the show she doesn’t say ‘2 + 2 = 4’, because who knows what mayhem might be unleashed by such an utterance.

That Greer got it in the neck for saying what everyone who doesn’t have a degree in Queer Studies believes to be true shows how tyrannical the trans sensibility has become. She’s being hauled over the coals for stating a fact. For saying a bloke is not a woman. Up is not down. Black is not white. If you live in a society in which it’s a risky business to express opinions, that’s bad enough; if you live in one in which even saying factual things can see you being branded ‘bigoted’, then it’s really time to worry.

It’s hard to think of any other issue that’s as forcefielded from rigorous discussion as transgenderism. Anyone who raises a peep of criticism about the new cult of self-identification, where a man can now become a woman simply by declaring it, is liable to be shamed and hounded and Twitch-hunted, which is when self-righteous Twits set up a Change.org petition demanding you be exiled from polite society for having said something that offended them.

Greer has fallen foul of the new speech-policing tranny state before. Last year, students at Cardiff University tried to have her banned from speaking on the basis that her ‘transphobia’ makes her a disgrace to ‘feminism and society’. Greer’s fantastically antipodean response was to say, ‘Just because you lop off your dick and then wear a dress doesn’t make you a fucking woman’.

Firebrand feminist Julie Bindel is continually hounded off British campuses, for the speechcrime of having written an article 10 years ago in which she said: ‘I don’t have a problem with men disposing of their genitals, but it does not make them women’. Thinking men are not women is the great thoughtcrime of our times.

In the media, too, commentary on trans stuff is tightly policed. When I wrote a piece for the UK Telegraph questioning the idea of an ever-expanding ‘gender spectrum’, the inevitable Change.org petition sprung up, saying the article was ‘disgusting, completely offensive, and should be removed at once’.

It wasn’t removed. Julie Burchill was not so lucky. Her 2013 piece for the Observer, in which she described trans activists as ‘bed-wetters in bad wigs’, was expunged from the Observer website at the behest of a mob of… well, bed-wetters in bad wigs, who gathered at the Observer offices to demand that it respect trans feelings by crushing its writers’ freedom of speech. Shamefully, it complied.

In Oz, the Courier-Mail felt the unforgiving sting of the morality police when it referred to a murdered transgendered prostitute as a ‘she-male’. The right-on went into meltdown. The paper was branded ‘absolutely disgusting’, even ‘dangerous’. Boycotts were organised.

The question one must always ask when debate is closed down or frozen as thoroughly as it is around the trans issue is this: what are you trying to hide? Censors are always trying to hide something. Censorship is about the suppression of awkward or inconvenient facts and ideas. It springs fundamentally from fear — fear that one’s pretensions or hypocrisies will be exposed. And this is the case with debate-allergic trans activists: they fear intellectual exposure.

It explains why they’re so incredibly hostile to feminists like Greer, who insist that being a woman is a rather more complicated affair than simply putting on some lippy and saying ‘I feel like a woman!’, as Bruce Jenner, Bradley Manning and other people with penises have done.

Greer’s insistence that womanhood is a social, historical, relational, biological thing, a thing of substance, a thing of flesh and bone and experience, is threatening because it calls into question the utterly subjective and relativistic politics of identity upon which the trans ideology is built.

The engine of the trans movement, and other identity movements, is not liberation but relativism. The motor of frenzied gender re-identification is the collapse of objective fact; the demise of measurable categories; the fraying of reason itself. In a West in which ‘the truth’ always comes with scare quotes, in which all cultures are treated as equally valid, in which criticising Islam has been rebranded a phobia and bigging up the Enlightenment is likely to see you called a racist, even the categories of ‘man’ and ‘woman’ are falling apart. Even the most concrete categories in human history, male and female, the categories from which we garner so much of our understanding of the world and each other, have been sacrificed at the altar of relativism.

It’s spinning out of control. Women’s colleges in the US are being swamped by men who identify as women. Facebook now has 71 gender identities to choose from. New genders are invented every day. One list of ‘genderfluid experiences’ includes ‘aerogender’ (where your gender is influenced by your surroundings) and ‘systemgender’ (‘a gender that is the sum of all the genders within a multiple or median system’ — you what?). What madness is this? It’s the madness of a society in which definition, and reality itself, counts for nothing in the face of people’s narcissistic, made-up identities, which they then demand that the rest of us celebrate, or else. Authoritarianism, you see, is a close cousin of relativism; relativism says ‘anything goes’ except for judgement and criticism — they must be crushed.

This explains the fury with Greer. In making that seemingly simple remark — that male truck drivers are not women — she reminds us that there are categories, facts; that there is a reality. And that is a revolutionary thing to do in these swirling, unanchored and frankly potty times.