It should be noted that a huge percentage of Australia is desert, arid and semi-arid land that barely gets any rainfall. It's sparsely populated because nobody wants to live those areas. There are huge challenges in day-to-day life in rural Australia and that lifestyle is not for everybody - especially new migrants who aren't used to that way of life. Using the existence of that space as justification for perpetual immigration is a poor excuse in my mind, unless we plan on building new towns and cities inland with infrastructure similar to that of the coastal cities.