Greens are the enemies of liberty. Environmentalists want to curb our freedom far more than the government's anti-terrorist laws ever will Brendan O'Neill Imagine a society where simply speaking out of turn or saying the "wrong thing" was openly discussed as a crime against humanity, and where sceptics or deniers of the truth were publicly labelled "criminals", hauled before the press and accused of endangering humanity with their grotesque untruths. Imagine a society where even some liberals demanded severe restrictions on freedom of movement; where people campaigned for travelling overseas to be made prohibitively expensive in order to force people to stay at home; and where immigration was frowned upon as "toxic" and "destructive". Imagine a society so illiberal that columnists felt no qualms about demanding government legislation to force us to change our behaviour; where the public was continually implored to feel guilty about everything from driving to shopping – and where those who refused to feel guilty were said to be suffering from a "psychological" disorder or some other species of mental illness". Surely no one would put up with such a society? Yet today, all of the above things are happening – under what we might call the tyranny of environmentalism – and people are putting up with it. In the current debate on liberty, we hear a lot about the attack on our democratic rights by the government's security agenda, but little about the grave impact of environmentalism on the fabric of freedom. It seems to me that green thinking – with its shrill intolerance of dissenting views, its deep distaste for free movement and free choice, and its view of individuals, not as history-makers, but as filthy polluters – poses a more profound threat to liberty even than the government's paranoid anti-terrorist agenda. Environmentalists are innately hostile to freedom of speech. Last month James Hansen, one of the world's leading climate change scientists, said the CEOs of oil companies should be tried for crimes against humanity and nature. They have been "putting out misinformation", he said, and "I think that's a crime". This follows green writer Mark Lynas's insistence that there should be "international criminal tribunals" for climate change deniers, who will be "partially but directly responsible for millions of deaths". They will "have to answer for their crimes", he says. The American eco-magazine Grist recently published an article on deniers that called for "war crimes trials for these bastards… some sort of climate Nuremberg." It is the mark of shrieking authoritarianism to look upon dissenting views not simply as wrong or foolish, but as criminal. Throughout history inquisitors and censors have sought to silence sections of society by labelling their words as "dangerous" and a threat to safety and stability; now environmentalists are doing the same. Their demonisation of sceptics as "deniers" has had a chilling effect on public debate. The environmentalist ethos is hostile to free movement, too. Behind the greens' attacks on road-building and cheap flights there lurks an agenda of enforced localism. What most of us experience as a liberty – the ability to drive great distances or to travel overseas, something our forebears only dreamt of as they spent their entire lives in the same town – has been relabelled under the tyranny of environmentalism as a "threat to the planet". The Optimum Population Trust, which counts Jonathon Porritt among its patrons, says mass immigration is "a route to environmental collapse". It believes the UK is overpopulated and wants to "balance immigration with emigration". Not surprisingly, opportunistic anti-immigrant outfits have borrowed elements of this argument. The British National Party now argues that "our countryside is vanishing beneath a tidal wave of concrete" as a result of house-building for immigrants. "Immigration is creating an environmental disaster", the BNP says. But perhaps the main way that environmentalism undermines the culture of freedom is by its ceaseless promotion of guilt. In the environmentalist era, we are no longer really free citizens, so much as potential polluters. We are continually told – by government, by commentators, by radical activists – that everything we do, from wearing disposable nappies to using deodorant to allowing ourselves to be cremated, is harmful to our surroundings. Liberty – true liberty – requires that people see themselves as self-respecting, self-determining subjects, capable of making free choices and pursuing the "good life" as they see fit. Today, by contrast, we are warned that we are toxic, loaded, dangerous specimens, who must always restrain our instincts and aspire to austerity. This is not conducive to a culture of liberty; indeed, it represents a dangerous historic shift, from the Enlightenment era of free citizenship to a new dark age where individuals are depicted as meek in the face of more powerful, unpredictable forces: the gods of the sea, sky and ozone layer. And what of those individuals who say "to hell with environmentalism" and continue living the way they want to? Apparently, in the words of the Ecologist, they have a disordered "psychology"; they are victims of "self-deception and mass denial". Some greens openly admit they are on the side of illiberalism. George Monbiot describes environmentalism as "a campaign not for more freedom but for less". Environmentalism is instinctively and relentlessly illiberal, and it is doing more to inculcate people with fear, self-loathing and a religious-style sense of meekness than any piece of anti-terror legislation ever could. If you believe in freedom, you must reject it.