What's wrong with the brain drain (?)

One of the characteristics of the relationship between the developed and developing worlds is the 'brain drain'- the phenomenon by which expertise moves towards richer countries, thereby condemning poorer countries to continued comparative and absolute poverty. It is tempting to see the phenomenon as a moral problem in its own right, such that there is a moral imperative to end it, that is separate from (and additional to) any moral imperative to relieve the burden of poverty. However, it is not clear why this should be so - why, that is, there is a moral reason to stem the flow of expertise in addition to seeking to improve welfare. In this paper, I examine three explanations of the putative moral aspect of the brain drain.