Australia is a huge country that is, while mostly desert, is also mostly empty. Its hard to comment on the ability of the social welfare system to support large numbers of migrants, there certainly is a large amount of space in which to put them. Australia is an immigrant country, it probably can handle some more.
I do not agree that the Australians should be able to keep the migrants. I think that it really may not be their right to decide whether they can keep them. It feels like it really limits the freedom on migrants if they don't have a say in the matter. I don't think they should be able to do that.