1) Zero net population growth is as much about preserving good standard of living for the children of former immigrants as it is about preserving it for the children of British descendants.

2) Let us not confuse multiculturalism with wholesale re-colonisation which is what current immigration policies amount to.

"If immigrants are made to feel somehow they are the cause of problems other Australians face, this sets up a very dangerous basis for the debate". The whole issue of a sustainable population is simply diverted by the origins of the people! Unless we are indigenous, and even many indigenous people are of "mixed" heritage, then this applies to us all. The issue is NOT about race, ethnic origins, nationality, but of numbers. Australia is already multicultural.
Keeping our numbers stable and sustainable is not racist, and this is simply a tool to keep the debate under wraps. Considering 2/3 of our population growth is from immigration, and also a similar proportion of our "natural" growth, then the topic of immigration cannot be avoided. If we "offend" foreigners, so be it!
It can't be assumed that recent immigrants want more people in Australia either. The public aren't consulted anyway. The Immigration Department consults with business elites, not the public.

Multiculturalism is a side issue from the issue of population numbers. Multiculturalism may or may not have merit in its own right (I personally prefer the concept of multiracialism rather than multiculturalism) but the bottom line is that it is an environmental question: how many people can this nation (or the world) support at a certain standard of living? Doesn't really matter whether they are black, brown or white. Nature doesn't care. Right now almost every environmental indicator in Australia is going down, that is, we are not living sustainably. So we have to stop, take a deep breath, and work out how we will reduce our impact on nature. What do we address? Technology? Population? Consumption? How about all three.