There are a number of ways in which the issue of immigration is connected to social justice and equity in rich and democratic nations like Australia. There is one set of factors that argues that such countries should have liberal immigration policies while there are others that argue for limiting immigration.
The main argument for a liberal immigration policy is that all people of the world deserve to have certain human rights. People deserve to have the chance to make a decent living. They deserve to be free from the fear of an oppressive government. For many people of the world, one or both of these things is not available in their home countries. Therefore, in order to treat all people with justice and equity, rich countries like Australia should open their doors to others, regardless of their race, religion, or other factors.
The main argument against such a policy is that it denies equity, and to some extent justice, to people already in the rich country. If Australia lets in many Asian immigrants, people already in Australia might suffer. Australians who are less educated and less skilled will see their wages and job opportunities decline in the face of immigrant competition. Australians who are more well-off might see their taxes rise if the immigrants need assistance. In other words, allowing relatively unlimited immigration puts burdens on the people already in Australia. This can be seen as less just and equitable.