The problem I see with that is one of numbers. The world population continues to increase at an alarming rate. Not only are absolute numbers increasing, but so too the rate of increase has risen dramatically over the past century. So there's lots of people around and plety more being born.
But not in Australia. Australia along with many other developed countries does not have a sufficient birth rate to sustain its own population. And that birth rate continues to fall for various reasons (anecdotally the housing boom being one of them since it's no longer possible for many couples to afford both a house
and kids). This trend shows no sign of reversing and, given the worldwide situation, there is no pressing need for it to do so. There's plenty of people, just not here.
And so the logical means of maintaining Australia's population is ongoing immigration. We need them more than they need us and our economy will suffer greatly if the population enters a serious decline, which it would without immigration.
We have already seen in Australia an unplanned experiment with population decline (Tasmania late 1990's). It came to the point of ordinary blue collar workers sitting literally alongside ex-premiers and current politicians, business leaders and even students and the unemployed at public meetings discussing the economy and what to do about the situation. I think that says enough about what happens economically when the population falls. Western economic systems simply aren't set up to cope with decline. It's was bad enough in one state whilst the national economy was booming, just contemplate what would happen if the decline were national.
So I think we ought to continue with immigration unless we can devise some alternative economic system which functions adequately with permanently negative GDP "growth" (that is, permanent recession) and the reality that increasing numbers of empty houses with no prospect of filling them would likely induce a house price crash (simple supply and demand). A complete redesign of the economic system which is presently based upon the notion of continuous growth (I acknowledge that the merits of this are highly questionable).
That said, the immigrants Australia
needs are the young and economically productive. That's not to say that we shouldn't accept others on humanitarian or other grounds, but the ones we actually need are those willing and able to work.