"Allowing skilled emigration is stealing human capital from poor countries."
No. Many of the same countries courted by the United States through aid and trade deals complain bitterly of the "brain drain" of their doctors, scientists, and engineers to the United States and other rich countries. If correct, these complaints would mean that current immigration policy amounts to counterproductive foreign policy. Thankfully, however, the flow of skilled emigrants from poor to rich parties can actually benefit both parties.
This common idea that skilled emigration amounts to "stealing" requires a cartoonish set of assumptions about developing countries. First, it requires us to assume that developing countries possess a finite stock of skilled workers, a stock depleted by one for every departure. In fact, people respond to the incentives created by migration: Enormous numbers of skilled workers from developing countries have been induced to acquire their skills by the opportunity of high earnings abroad. This is why the Philippines, which sends more nurses abroad than any other developing country, still has more nurses per capita at home than Britain does. Recent research has also shown that a sudden, large increase in skilled emigration from a developing country to a skill-selective destination can cause a corresponding sudden increase in skill acquisition in the source country.
Second, believing that skilled emigration amounts to theft from the poor requires us to assume that skilled workers themselves are not poor. In Zambia, a nurse has to get by on less than $1,500 per year -- measured at U.S. prices, not Zambian ones -- and a doctor must make ends meet with less than $5,500 per year, again at U.S. prices. If these were your annual wages, facing U.S. price levels, you would likely consider yourself destitute. Third, believing that a person's choice to emigrate constitutes "stealing" requires problematic assumptions about that person's rights. The United Nations Universal Declaration of Human Rights states that all people have an unqualified right to leave any country. Skilled migrants are not "owned" by their home countries, and should have the same rights to freedom of movement as professionals in rich countries.