Optimal Migration: A World Perspective
"We ask what level of migration would maximize world welfare. We find that skill-neutral policies are never optimal. An egalitarian welfare function induces a policy that entails moving mainly unskilled immigrants into the rich countries, whereas a welfare function skewed highly towards the rich countries induces an optimal policy that entails a brain-drain from the poor countries. For intermediate welfare functions that moderately favor the rich however, it is optimal to have no migration at all."
Like the Bud, I'm blown away by the question: a world perspective on migration. It's the right question. It's so, so difficult to ask.