The dangers come from left, right and centre; and the development of internet platforms that run alongside mainstream media.

Let's start with the left. The left has adopted multiculturalism with fervour, which is fine, up to a point. Of course, we should respect other cultures, religions and languages and allow them to be practiced, used and celebrated.

But that could and should continue to flourish even if Australia had zero population growth and no net immigration. The problem is that the left has allowed its meritorious promotion and defence of multiculturalism and support for refugees to be confused with immigration and population policy.

It brands any rational call for lower immigration to be an attack on multiculturalism, or worse as outright racism. That is perhaps why the Greens do not have a population policy and do not speak out about the effect a larger Australian population is having on the environment.

In a way, however, this left position has itself a hint of racism in it. Let me explain. People who advocate for a sustainable population policy in Australia do it with the best interests and future of all the Australian people at heart, whether those people are white, yellow, brown or black, whether they speak English or another language at home, or whether they are Muslim, Christian, Jewish, animist or atheist.

On the other hand, those people who reject cutting back immigration because they support multiculturalism and because they say such a cut would be in favour of a white, Christian Australia are behaving in a way which is in fact inimical to the best interests of multicultural Australia. People who support high immigration damage Australia as a whole and with it the quarter of Australians born overseas and many more with parents born overseas or who speak a language other than English at home or practice a religion other than Christianity.

But once a viewpoint becomes an established view of the left, it is extremely hard to dislodge. Unless that multiculturalism-high immigration nexus is cut, the case for a sustainable Australian population is doomed.

Now let's turn from the left to the far-right, which is even more dangerous to the prospect of sustainable population, even though it wants to limit immigration. That is because One Nation and others like them who support lowering immigration do so for the wrong reason: they say they want to protect white Christian Australian values. For example, they want to end "Muslim immigration".

This is the unacceptable face of the lower-immigration argument. It is such an unacceptable face that it overwhelms sensible lower-immigration arguments and anyone who puts them runs the risk of being branded a racist - even if their arguments have nothing to do with race but solely about the environment, infrastructure costs and the impact on agricultural land.

Worse, the far right's view and the left's view feed off each other like some symbiotic growth monster.

The more the far right rants, the more the left cannot separate population from multiculturalism and support for refugees. The more the left support refugees and multiculturalism the more xenophobic and unacceptably racist the far right becomes. And the profoundly sensible non-racist arguments for a sustainable population policy get drowned out.

One of the reasons these positions feed off each other is the rise of social media. These days everyone can be a publisher to the world for free. Before the internet, people with minority views of any kind found it hard to get heard in the media. Now they publish themselves and get heard, even if only by a few, who then echo the sentiment.

Worse, mainstream media pick it up. They do so because media professionals have long had a respect for publication. Something published had gravitas. That may have been true pre-internet, but it is not true now.

The far right is infected by anti-expertism. The hard, expertly produced facts of climate science and ecology are held by many on the far right as "alternative facts" and that their denialist view is equally valid.

Now let's turn to the centre. The two main arguments from the centre in favour of high immigration are ageing and the skills shortage. Both are furphies, but they resonate; surely young immigrants will save us from the costs of the ageing population and our economy depends on jobs.

But the facts show these are non-solutions. The way to deal with the ageing population is the same way a python deals with a swallowed goat: you just wait for the lump to naturally pass through to the end of the age-based demographic bar chart.

It would take an enormously counter-productive amount of immigration to have any significant change on the age profile of the Australian population. But to run that argument would be beyond the statistical capability of the great majority of the population. You would need at least year 11 maths.

The population's lack of statistical and mathematical education is another stumbling block for the promotion of a sustainable population. It is coupled, unfortunately, with widespread ignorance about immigration levels and population growth. This is evidenced by the persistently high percentage of poll respondents who have answered that immigration is "about right", whether the level at the time was 70,000, 100,000 or 190,000.

Ageing and skills arguments are exploited by those who get richer through high immigration at the cost of everyone else.

On jobs, Australia's unemployment rate hovers around 5 per cent and underemployment hovers around 9 per cent. So there is no labour shortage, just a shortage of employers willing to train people already here. And no shortage at all of employers who prefer to depress wages by bringing in lower-paid workers and increasing the labour supply. This is why wages have stagnated in Australia.

Big retailers, property developers, big agriculture, big pharma and financiers love high immigration, even if the Ponzi scheme looks as if it is coming to its day of reckoning. The wages stagnation has now hit retail and property markets. Profits and property prices are at risk.

Nonetheless, Australian governments continue to set high immigration quotas each year because they are utterly beholden to their big-business donors.

So what is to be done?

Perhaps the most important thing is not to concentrate solely on promoting sustainable population, but to deal also with some of the institutional deficiencies that have resulted in Australia having an unsustainable population policy.

Perhaps the single most important is the law relating to political donations.

If you allow them, big business will always take the lazy way to big profit by throwing a few pennies in bribes to the major parties to continue high immigration.

Australia will never get a sustainable population policy until all corporate political donations are banned and all individual donations are recorded as they happen on the internet in an easily accessible form and that all cash donations are also banned.

Then, the completely misguided nexus between multiculturalism and refugees on one hand and immigration on the other must be broken. We should have a Minister for Social Inclusion and a separate Minister for Population.

Then we have to engender more respect for independent experts in an age when, alas, every Tweet is seen as equally valid.

Not easy. But not impossible.