The businessman and environmentalist Dick Smith is in a dispute with the ABC about the way his views on immigration have been reported. We make here no comment on Mr Smith's argument with the ABC, which in any case is well able to defend itself. Nonetheless the nature of the dispute does raise a wider point about the current state of debate in Australia.

In brief, Mr Smith argues for a cut to the immigration intake to about 70,000 – levels seen during the Hawke and Keating years – although within that reduced number, he is suggesting that the refugee intake should be increased. His reason: if immigration continues at the current level (about 190,000 permanent migrants a year, plus about 17,000 under Australia's humanitarian program) it will increase Australia's population to a size that the continent's environment cannot sustain.

Australia, a land of immigration.

His point about sustainability is valid and should be up for discussion. It has been the subject of a number of studies, not least by CSIRO researchers, which have attempted to assess the effect of different rates of immigration on a range of variables: food and water supplies, other resources, cities, the natural environment, and so on. These are important questions. At present though, discussion of immigration's likely effect on Australia's environment is drowned out in the far louder, more rancorous argument about the fate of asylum seekers. Immigration has become an either-or issue. All nuance is stripped away into a polarised debate. Anyone who like Mr Smith tries to explain a moderate and rational basis for limiting immigration can find themselves lumped together indiscriminately at one pole of that debate with lurid xenophobes and racists. Inquiry is silenced. Important issues, caught in no man's land between two entrenched extremes, may not be discussed.

The same effect, the same silencing of common sense and abandonment of centrist positions, can be seen too in the wider debate about conservation, climate change and the environment. Conservation one might think would be a natural concern of those who call themselves conservatives. (Indeed, an organisation exists called Conservatives for Conservation, though its impact is yet to be felt.) The right-of-centre philosopher Roger Scruton has written a compelling argument that conservation should properly be considered a conservative cause.

Preservation of the environment should in theory depend to a great extent on the action of the mainstream of the population – that is, the middle class. It is not that poor people don't care about environmental issues; rather, that income pressures will often hinder them from political action – like environmental activism – which has objectives outside their immediate economic advancement. It is the middle class who more often than not have the income, the education, and the resources to take up the cause of the environment. The attitudes of that middle class also more often than not lie towards the centre of the political spectrum, not at the extremes.

In this country however, debate about the environment, and specifically climate change, has retreated to those extremes. On one side are the Greens, who in NSW are dominated by a radical socialist group that sees environmentalism as a Trojan horse it can use to undermine the entire capitalist economic system. The party is ballot-box poison as a result, confined to the fringes with about 10 per cent of the vote. On the other side are various anti-green, anti-climate science, pro-coal agitators within all the major parties. The Prime Minister – possibly against his better judgment, although it is hard to tell these days – is now working with them. His attempt to get AGL to keep the clapped-out Liddell power station operating for five more years is only the latest absurdity to which he has had to stoop in obedience to the lobby dominant in his party and coalition. Labor, which is beholden in part to coal miners, is also compromised, though for different reasons. We acknowledge that in both Labor and the Coalition there are many who know the environmental issue, grasp its importance, and want their concerns to be reflected explicitly in platforms and policies that lead the agenda. But they are not in charge.

That leaves a very large group of voters, moderate and centrist in outlook, who are deeply concerned about the environment and climate change, who don't want to be labelled racists if they express legitimate concerns about immigration, who believe environmental policies should aim to save capitalism from itself, not destroy it, and who are not represented adequately by either major party. Our system and our politics are failing them.