Every American school shooting gives rise to hand-wringing debates about how "gun culture" and violent Hollywood movies are warping young people's minds. Usually the finger of blame is pointed at the Charlton Heston set, those swaggering Marlboro men who insist on their right to bear arms.

However, there has been a reluctance to discuss what might have warped Pekka-Eric Auvinen, the 18-year-old Finn who shot seven of his fellow pupils, his headmistress and then himself in a school in southern Finland last week. Maybe that's because Auvinen was not acting out some bizarre Die Hard-style fantasy, but rather seems to have fancied himself as the armed wing of contemporary environmentalism.

We'll never known for certain what pushes young men from quite cushy backgrounds to go on a shooting spree. There is evidence that Auvinen liked Quentin Tarantino films and was obsessed with the Columbine school massacre. Yet if we take him at his word - the thousands of words he spoke in his rambling YouTube videos and online manifestos - it seems he was also deeply agitated by humanity's allegedly noxious impact on the planet.

Shortly before the massacre, he made a tribute video for Pentti Linkola, a well-known Finnish intellectual and deep ecologist who believes the planet is vastly overpopulated by human beings. Auvinen's tribute video quotes some of Linkola's misanthropic statements: "That there are billions of people over 60kg on this planet is recklessness"; "The most central and irrational faith among people is the faith in technology and economical growth"; "A minority can never have any other effective means to influence the course of matters but through the use of violence"; "I wish that death to mankind comes soon."

Auvinen, whose own mother is an ecologist and has written for a Elonkehä, a deep-green magazine that Linkola also writes for, seems to have taken these extreme ecological views to heart. In one of his online manifestos he declared: "death and killing is not a tragedy ... Not all human lives are important or worth saving." He said: "Humans are just a species among other animals and world does not exist only for humans." He warned of his plans to launch "one man's war against humanity, governments and weak-minded masses of the world."

In one of his online videos, Auvinen wore a T-shirt saying "humanity is overrated". This could be the slogan of today's extreme environmentalist movement, which only sees humanity in terms of its "carbon footprint" and destructive impact on the planet. That slogan comes not from a violent Hollywood movie or gangsta rap track but from an American series beloved of liberal TV viewers: House, in which Brit actor Hugh Laurie plays a cynical doctor who saves human lives despite not being a great fan of humanity.

Auvinen declared himself to be an "antisocial Social Darwinist". He was part of a nihilistic group of social Darwinists in southern Finland who believe that the Darwinian concept of natural selection should be applied on a societal scale, so that only some humans - presumably eco-enlightened ones - will survive. In declaring a "one-man war against humanity," was Auvinen trying to do his bit to fight overpopulation, to bring about "the death of mankind" that one of his heroes, Linkola, talks about?

It is tempting to view misanthropes like Linkola as one-off crackpots, and school shooters like Auvinen as simply deeply disturbed individuals. And thankfully, school shootings are still exceptionally rare, even in America. Yet the truth is that Linkola, as echoed by Auvinen, only expresses fairly mainstream ideas in a more violent and gruff fashion. When Linkola, as quoted by Auvinen, says that the existence of "billions of people over 60kg on this planet" is recklessness, he is giving voice to the widespread idea that we have overpopulated the Earth. From posh and respectable Malthusian outfits to serious commentators, many today argue that population control is the only solution to humanity's "carbon footprint". Shooting dead eight people is a kind of population control, is it not? Auvinen seems to have thought so.

When Linkola, as quoted by Auvinen, says it is irrational to have faith in technology and "economical growth", and also that "material prosperity doesn't bring anything else than despair," he is expressing a widely held loathing of economic development. Many serious thinkers and writers argue that wealth makes us unhappy, and that "the drive to make more money than you could possibly need, to buy more goods than you could possibly enjoy, is a species of mental illness."

Linkola may sound like a crank, and Auvinen must have had some serious problems to go on a shooting spree. But the ideas that seem to have been held by them both - that humans are effectively an alien species overcrowding the planet, who irrationally believe in progress - are standard fare in mainstream western debate today.

This is not to argue that Linkola is in any way responsible for what Auvinen did. Nor is it an argument for censoring or in any other way restricting the views of deep ecologists and western misanthropes, however foul they may be. Auvinen alone is responsible for the monumental tragedy that occurred in southern Finland. But if this school shooting is "not to be in vain," as people frequently say after tragic events, then surely we owe it to ourselves to explore the possible link between today's mainstream Malthusian notion that mankind is destroying the planet and the rise of a new form of anti-humanist nihilism.