Donald Trump’s characteristically blunt remarks on immigration have, predictably, provoked widespread outrage from foreign governments and the media, but they raise an important issue that needs serious discussion.

The issue is not whether some countries are, or are not—to use the colorful language attributed to the president—“shitholes.” As much as their governments may protest, the people so desperate to leave these countries might well agree with Trump’s characterization. The issue is, rather: Who should be allowed to immigrate to the United States?