She looks both younger than her age and old enough to have the cares of the world on her shoulders. Face scrubbed clean, dressed in a severe black jacket, Greta Thunberg stares unsmiling from the cover of this month’s GQ magazine. It’s an arresting, even unsettling, image: her outstretched finger points accusingly at the reader, in the manner of a wartime recruitment poster. Your planet needs you, millennials.

Back in the 1990s, posing for men’s magazines in your knickers was a rite of passage for young actors and pop stars not so much older than Greta, but that feels a very long time ago now. Here is a cover girl designed not to titillate male readers but to nudge their consciences, and very successfully, too. Successfully enough to make her some powerful enemies.

The perennial rightwing agent provocateur Arron Banks this week tweeted, “Freak yachting accidents do happen in August”, over a picture of Greta sailing across the Atlantic in order to avoid the carbon emissions of flying. A joke, he insisted, but what’s funny about the idea of a teenage girl sinking to the bottom of the sea?

Something about female eco-warriors seems to bring out the worst in a certain kind of man, whether it’s Nigel Farage accusing Meghan Markle of destroying Prince Harry’s popularity with her woke enthusiasms, or the Australian shock jock Alan Jones suggesting this week that the New Zealand prime minister, Jacinda Ardern, should have a “sock shoved down her throat” for daring to argue that Australia go further in reducing emissions. Choke her, drown her, whatever; just shut her up. Who do they think they are, these women telling us how to live?

Greta Thunberg sets sail for New York on zero-carbon yacht Read more

It’s not just men who bait climate crisis campaigners, of course; the TalkRadio presenter Julia Hartley-Brewer tweeted this week, over a picture of Thunberg at sea, that she’d just booked flights for a winter sun holiday with “level of guilt being felt: zero”. Male environmentalists get their share of vitriol, too – even if it’s hard to recall, say, Zac Goldsmith being targeted in quite this way.

It’s selfishness, rather than misogyny, that is surely the root cause of this rage at the very idea of being asked to give up any individual freedom – to fly, drive, eat a steak, carry on with our oblivious lives as if nothing was happening – for the greater good. But female climate campaigners are perhaps uniquely prone to press the buttons of what might be called toxic libertarians; people who combine a burning desire to do what the hell they like with fury at the very idea of being nagged, nannied or told what to do, especially by women. We are way beyond arguing about the science here, and fast moving beyond politics too, at least in the conventional sense of debating how far and how fast it’s reasonable to move in a democracy, or whether the moral absolutists of movements such as Extinction Rebellion have thought hard enough about the impact on other people’s livelihoods.

There is still a perfectly legitimate political argument to be had about the need to secure democratic consent for sweeping changes in people’s lives. But those arguments are giving way to something altogether nastier: not climate crisis denial, so much as climate crisis nihilism. The nihilists don’t necessarily deny that the planet’s frying but, essentially, they refuse to feel bad about it; they want their sunshine holidays and their 4x4s, come hell or (possibly quite literally) high water, and screw anyone who gets in the way.

Play Video 2:46 'This is an emergency': Greta Thunberg speaks at Guardian Live – video

If Brexit is any guide – and there is an interesting overlap with the sort of hard Brexiters who no longer argue for no deal on its merits, but solely on the grounds that it’s what they wanted and they’re damn well going to have it – they will increasingly use social media to bully their opponents out of the public sphere and embolden their supporters. We are watching a new front open up in the culture war, and its timing is probably no coincidence.

Without the new lease of life it gives them, where exactly would the self-styled bad boys of Brexit be now? Banks, the money man of the movement, is currently under investigation by the National Crime Agency over the source of loans made to leave campaigners. The emergence of a hard-Brexit Tory leadership threatens to deprive Farage’s Brexit party of its entire raison d’être. He and his hangers-on need a new rallying cause and this one looks like a perfect fit, since his followers tend to be apoplectic about anything – smoking bans, speed cameras, sugar taxes, hate speech laws or simply woke millennial sensibilities – that threatens to restrict individual freedoms in the greater good. Any outrage generated by personal attacks on environmentalists just gives them the welcome oxygen of publicity, which is why it’s generally wiser to ignore it. But dragging a 16-year-old into this splenetic, self-serving bar brawl makes a dangerous new level of provocation that should not go unchallenged.

Greta Thunberg’s unique strength when she first emerged as an activist was that, as a child, and one with Asperger’s to boot, she had almost unassailable moral authority. Her critics argued that if she was old enough to tell world leaders what to do then she should be old enough to take the heat for it, but most people recognise that hers is still an innately vulnerable age; not quite a child, not quite grown up, instinctively evoking protective feelings in anyone with an ounce of humanity.

That doesn’t mean elected politicians are required to treat her every utterance as a tablet of stone, but initially even her detractors accepted that to argue back as robustly as one might with an adult would seem bullying and unkind. It is a twisted testament to her success that the gloves have now come off with a vengeance, but it’s frightening all the same.

Even as someone who sympathises with Thunberg’s argument, admiring her courage and imagination, for a while I have felt a creeping unease about where this is all going. She is still so young, so vulnerable, for someone carrying such an impossible weight of expectation. How would she cope if the world leaders who have paid lip service to her demands don’t ultimately do what she wants? Will she one day regret having missed out on a more conventional adolescence?

But the violence of the backlash adds a more worrying dimension. If she were my daughter I would be both immensely proud of her, and terrified for her; torn between not wanting her to be bullied into silence, and wanting to hide her away from it all.

Yet however her parents choose to deal with this, the broader problem she highlighted remains. A society that cannot bear to be lectured by its children, even when they’ve got a point, while the adults are behaving like spoiled toddlers refusing to clean up their own mess, is one that can never progress. Perhaps our children can finally be children again, when the rest of us grow the hell up.

• Gaby Hinsliff is a Guardian columnist

• This article was amended on 19 August 2019 because an earlier version misnamed the New Zealand prime minister, Jacinda Ardern as Jacinta Ardern. This has been corrected.