The opposition to mass-immigration (the country is growing at about 1.6% annually, with the same annual level of immigration as the UK, a country with 3x the population) is completely justified and it is not in the long-term interests of the country or of individual Australians.
Its not only the formal mechanics - the whole system is rorted, with a lot of fraud. A Chinese businessman bribing federal politicians for citizenship is a current news item.
Finally Australia makes its way in the world by mining and selling off its fixed endowment of minerals. The rest of the economy is not particularly competitive, mostly just domestic services and real estate. More people means a smaller slice of natural resources per person. This is not theoretical - wages are flat and cost of living pressures are high in the country. Public healthcare, education and transportation are all overcrowded.
By contrast the prior #1 most liveable city - Melbourne - has grown from 2 million 30 years ago to 5 million currently, forecast to get to 8 million by 2050, all due to mass immigration. Livability has fallen directly in line with population growth.
I've lived in a lot of cities around the world and think there is a 'sweet spot' population number: big enough to allow the provision of niche services and the agglomeration of talent, yet not too big as to introduce costly dis-economies of scale (usually through very expensive housing and transportation.) That level seems to be about 1-3 million.