People immigrate between countries for opportunities. For opportunities which are denied to them for being born to a particular set of parents, economic background religious background and so on. Opportunities in a new land without prejudices he feels has been denied to him back home. It gives him/her chances to improve one's perceived sense of self worth and search for better standard of living, better paid jobs and a higher quality of life in terms of health and enjoyment.
For a person in space or from a different planet, it does not matter whether we are whites or blacks, from India, China or US, tall or short etc.. We are humans.. Let us go beyond all such claustrophobic prejudices and work for a better world.