The most significant point is one made in passing: that the only way to improve the lives of most of the world's poor people is to raise the standard of living in the countries where they live now. Encouraging the most skilled and educated people to leave those countries would actually hinder this process.
I might add that the most powerful force for raising standards of living has always been, and will always be, technological progress -- more and more useful things are invented and can be produced more efficiently and therefore more cheaply, while the amount of wealth that can be created per person steadily increases. This is how the countries which are now rich got that way. If you want people in the Third World to be better off, you should want to see technology move forward as fast as possible. This is most likely to happen if the developed countries that generate most innovation are not distracted by, and forced to divert resources to deal with, the social problems which excessive levels of immigration can cause.