Why can’t we just close off the border with Mexico? William Cavanaugh suggests a cynical explanation: We don’t want to, because they serve an essential purpose.

A porous border does what neither an open border nor a closed border can do. Closed borders would keep out the laborers we need to keep some industries running efficiently. Opening the border would give migrants stability and rights, and make them less controllable. By maintaining some control, but not so much, we get our cheap labor and keep them in liminal vulnerability.