Bumping up our population by adding a million every 3&frac12; years leaves most Australians cold.  They have nagging doubts about what is the world's biggest immigration program, the developed world's highest population growth. 
One reason for public suspicion is that advocates of a Big Australia never come clean about the details - for infrastructure, for density, for a degraded environment. 
Here are my three challenges for supporters of a Big Australia.
First, they should link their population build-up to infrastructure.   
Right now, they wave it away, saying "Oh it's all a matter of infrastructure", as if this had never been thought of. But even massive infrastructure spends by states is only keeping pace   with 80,000 to 100,000 added to both Sydney and Melbourne each year. 
Not one of the Big Australians - the Business Council for example - has said that for every additional 25,000 migrants above a certain benchmark in any capital the commonwealth must fund 10 kilometres of inner city underground or light rail or bus transit-way.  In turn, the commonwealth might require the states to reserve corridors.  State and commonwealth governments should be able to guarantee Australia would not be laying out new suburbs that leave residents beyond easy walking distance from public transport.
Business lobbies and conservative think-tanks want the capitalist free-for-all that goes with rip-roaring numbers. But they don't want any hike in public spending, tax and borrowing. But face the fact:  high immigration brings either congestion or the heavy spending required to fix it.
My second challenge:  Big Australians need to get honest about the intensified zonings required as both Sydney and Melbourne climb to 7 million by mid-century.
Lack of candour on density was exemplified by former NSW premier Barry O'Farrell.  He declared his support for ambitious immigration figures.  But his biggest planning decision as premier was to kill off plans for 10,000 new units through rezoning along the north shore rail line in Ku-ring-gai.  Placing towers along a transport corridor (only six per cent of the council area) was sound planning.  With such dishonesty the joyful rhetoric about a bigger Australia is separated from discussion of the urban form needed to support it. 
Chris Johnson, the former Government Architect now with the Urban Taskforce, has drafted maps that show thick forests of towers around transport nodes like Hurstville or Parramatta.  He hopes the next step is an underground rail system linking them.  This is the kind of honesty I want. But two concerns open up:  first, we already have thick forests of residential towers. How much thicker might they be, at Chatswood or Strathfield for example, to accommodate a city of seven million?  And, second, what would be the time lag before the world's most extensive metro, an underground running from Bondi to Parramatta, gets installed?
Harry Triguboff is a sincere advocate of a Big Australia, probably none more.  In 2006 he suggested that Sydney's green areas should be opened up for development because there were too many forests and parks.  This vision of his elegant towers above the waters of Port Hacking or Pittwater was cheekily intended to provoke a premier proud of his parks. 
So in a similarly playful spirit I advance my own modest proposal: a re-zoning of Point Piper to lift its population from its current 6000 to a robust 30,000, pumping up its R2 zonings to allow stepped towers rising from, say, five stories on Wolseley Crescent reaching 30 in Wunulla Road.  Its most famous resident at number 46 declared, before he became Prime Minister, "Density is not the problem it's the answer."  The state's battering-ram planning laws would surely not be required to install these towers since Point Piper's residents contain many business leaders attached to the Big Australian vision and - I assume - eager to help accommodate the 50 to 100 million they long for so ardently.
Here's my third challenge to the advocates of Big Australia, one they're not even close to facing: link higher population growth to progress towards a sustainable Australia.  Spell out that any immigration above, say, 90,000 per annum would be dependent on certified progress in benchmarks such as stepped reductions in water use per head or carbon emissions per head.  Rapid population growth is making it harder to maintain recent progress.  More (treated) sewage means a bigger dump of nutrients into our rivers, more cars a rise in ground level ozone, more multi-unit dwellings, the return of harbour overflows.
But for advocates of Big Australia this nitty gritty is not heroic.  It gets in the way of their vision:  piling on a million more consumers every 42 months.
This Australia of erratic rainfall, thin soils and arid inland is being frogmarched to a high population future with slogans like "it's just a matter of infrastructure" or "density is not the problem."
With nobody spelling out the implications.
Bob Carr is a former NSW premier and foreign affairs minister.