For weeks, the most important question for police monitoring plans for a protest camp at Heathrow was where it would be. They now have the answer: a mile north of the airport’s northern perimeter in an unused playing field. Here, a few hundred climate change activists will, they say, spend four days fending for themselves and conducting workshops on global warming and how to combat it. They say their number should rise to about 1,500 by the end of the week. If so, police will outnumber them when their protest culminates in a day of direct action demonstrations, probably on Sunday. They have promised not to invade the runways.

Will they really bring the world’s busiest international airport to its knees? That depends on whether such a supposedly nonhierarchical gathering can make plans and stick to them. The expected attendance of veterans of G8 protests from several continents suggests it may not be able to. This would be unfortunate – for the cause they hold dear, the quality of climate change debate, and the future of free speech.

This protest is happening because aircraft are conspicuous carbon emitters (18 million tons of carbon dioxide a year from those fuelled at Heathrow alone) and they emit it at high altitude, where it is thought to trap more heat than at sea level. Even so, aviation can make a powerful argument for exceptional status in the struggle to reduce emissions. It has a unique claim to have changed the world for the better as a lubricant of global capitalism, a window on foreign cultures and a simple enhancer of lives, whether by enabling Alaskan schoolchildren to see the sun in winter, or allowing families separated by work, migration and marriage to keep in touch.

Mass air travel is not “binge flying”. It is the everyday miracle of our age. Tony Blair was honest enough to admit he was loath to stop taking holidays in the Caribbean. In doing so he spoke for millions genuinely anxious about climate change but understandably reluctant to forego one of the transforming experiences of their lives. He also knew, as his successor does, that London’s role as an international aviation hub is critical to Britain’s economic health. Last week’s warnings that continued chaos at Heathrow would take the shine off the City’s financial services supremacy came too late; it already has.

The climate campers should therefore be very realistic about the scale of the sacrifices they are demanding. They should also acknowledge that theirs is hardly a voice in the wilderness: not only has the High Court defended their freedom to protest even at the risk of airport disruptions by refusing to grant the broad injunction sought this month by BAA; aviation emissions are near the top of every major party’s policy agenda.

Direct action advocates will argue that this is their victory. As the Suffragettes proved, publicity stunts by a hardline fringe can make a ground-swell of calls for change seem moderate by comparison. But the Suffragettes posed no threat to the liberty of others. The moment the Heathrow activists resort to cutting through perimeter fences or leaving suspicious packages in terminal buildings, they will bring the airport to a standstill, deprive others of their freedom to travel and forfeit the right to be heard. The environmentally-concerned majority would be more impressed by cogent arguments for more efficient engines and, by all means, alternatives to air travel. If this is too much to hope for from the climate campers, they should at least keep their protest legal.