We report today that gay rights icon Peter Tatchell and other prominent figures on the British Left are currently the subjects of a bizarre and vicious witch-hunt by transsexual rights campaigners and their allies. “I’d like to tweet about your murder you f–king parasite,” wrote one anonymous tweeter to Tatchell over the weekend.

It’s worth taking a moment to consider how this extraordinary state of affairs came about. The row started when 150 of Britain’s great and good left-wing commentariat signed a letter in defence of free speech at university campuses in response to a number of proposed boycotts of those with opinions the notoriously intolerant and thin-skinned transgender lobby does not like. Trans campaigners have leapt on the letter as evidence of “transphobia” on the part of the country’s leading feminists, gays and lefties. Yes, it is absurd as it sounds.

Why is feminism splinter ing over trans issues and sex work? Where is unity over DV child care fgm reproductive rights equal for all of us? — suzanne moore (@suzanne_moore) February 15, 2015

At its heart this row is about a rift between those who believe that free speech and open debate are sacrosanct and those who cherish “safe spaces” in which offended groups need not hear debates that might traumatise them. My colleague Allum Bokhari has written persuasively about the intellectual history of this divide, which is currently being played out on university campuses, debate societies and online.

Classical liberals insist that the public good is only served by full and frank discussion, and that unfettered debate, free from worries about who might be “offended,” is the cornerstone of our way of life and central to our democratic values. Obviously, they are right. But the minority who reject debates that do not support narratives of oppression, victimhood and hurt feelings is very vocal, and in some cases quite powerful. They can also be exceedingly vicious.

What’s worrying about this minority is that it is populated by young, well-educated people who ought to know better, such as the former president of the Cambridge Union, Tim Squirrell, whose writing is indistinguishable from the authoritarian buzzword bingo you find in the Guardian’s comment pages. Squirrell himself is well-mannered, but he is uncompromising about his views that, for example, abortion debates should not be held on campuses if there’s a risk someone somewhere might claim to be upset by them.

Millennials are the least bigoted, least racist, least homophobic and least prejudiced generation in the history of the species. But the flip-side of this apparent generational tolerance is the unwillingness of some to examine dodgy assumptions and a refusal to listen to others–even if they broadly share the same, progressive views.

Squirrell’s opinions are rejected by the silent majority of students and by some others with platforms from which to point out the absurdity of universities banning pop songs and national newspapers, just as most ordinary people reject the censorious instincts of Guardian columnists. But those instincts are shared by many young people in student media and particularly in student unions, where puritanism and wacky politics have become a running joke to everyone except those passing the motions.

That the Left is now routinely attacking figures such as Peter Tatchell and radical feminist Julie Bindel is remarkable–and, in a dark way, almost funny. Bindel is one of the most prominent feminists of her generation and Tatchell is, of course, a justly revered gay rights icon. It is, similarly, mystifying that Germaine Greer should be such an object of scorn: apparently, she’s a “transphobe,” too.

As Bindel put it to me last night: “The nasty transgender misogynists – a tiny minority of trans folk – wish to punish feminists and send a warning to anyone else that dares to say what we know is true – that gender is a social construct, and that there is no such thing as a ‘real woman’ or a ‘real man’.

“They have attempted to destroy my reputation and ruin my career, not by democratic protest, but by bullying and threatening any sponsor, individual or organisation that hires me, wishes to give me an award, or asks me to speak. After 11 years it is clear that this is a sadistic witch hunt. I will never give in, and they will never win.”

Not everyone will agree with Bindel’s trendy analysis of gender as a social construct, but few can deny she has been subjected to a decade-long campaign of torment, ridicule and confected outrage because she puts the rights of so-called “cisgender” women–that is, women who were born women–above those of the transgender outrage circus.

The truth is, the jury is still very much out on transsexualism: the science is not settled on what kind of disorder it is or what treatments might best be administered. We know, for instance, that transition surgery does little to curb suicide rates, that transgender patients often present with other psychiatric problems, such as bipolar disorder, and that transsexuals are disproportionately poor compared to straights, gays and lesbians.

Beyond that, science is hampered by the framing of the transgender problem as a “civil rights” issue, so as to justify state spending on horrific and irreversible surgical procedures, rather than a mental health issue. In any case, so long as debate in public square is conducted on the basis of feelings, instead of facts, we may never know how best to approach the disorder.

Howls of outrage from Twitter mobs intent on policing such debates, even to the point of throwing fellow-traveller feminists and gay rights activists to the wolves, do nothing to help transsexuals and risk permanent damage to the integrity of free speech not just on university campuses, but in wider society, too.