Immigrants to Australia or New Zealand must be willing to learn English and should be from a background that will enable them to fit in and contribute to society. In Australia, Greeks and Italians came, learnt English and assimilated.
Bringing in people who won't obey the law and refuse adopt the values of their new home won't work. Japan, Singapore, and many Middle Easten countries won't allow a different race and culture to take over.
Saudi Arabia won't allow mass immigration of Christians and western culture, Japan doesn't want foreigners settling there at all, Singapore allows immigrants who will benefit the country but is carefull to maintain the current race ratios among the population i.e. currently 75% Chinese is going to stay that way.
Controlled, selective immigration is an enormous benefit to a country. Just look at the UK though as an example of what happens with uncontrolled mass movement of people.