Australia has built up infrastructure slowly and sensibly to suit our needs and within our means for generations. However over the last decades our Governments have been crush loaded that infrastructure to unsustainable levels with massive rates of immigration. Circa 200k per year of net overseas migration means more need for housing, roads, schools, hospitals etc. The population growth is happening so fast and without planning that we simply can't keep up the infrastructure and therefore the incumbent population's standard of living declines. Thus the massive debt being taken on board to try and keep up with the growth.
To be clear, I'm not saying lets cut all immigration, I'm saying it needs to be at a sensible level.
Here are a couple of articles that discuss just this subject:
