Greg Mankiw worries about the effect of a brain drain on the Indian economy, were the US to open its doors to skilled workers:
If skilled software engineers leave India for Silicon Valley, the unskilled workers left behind in India could well be worse off. Allowing more skilled workers into the United States might exacerbate global inequality, even if it enhances global efficiency.
I’m not convinced. “Brain drain” effects always seem to me to be more anecdotal than empirically proven. And if I recall correctly, one of the countries in the world which was most worried about a brain drain was Ireland. How did that work out?