Lant Pritchett argues forcefully that increasing labor mobility will reduce global poverty and points out the moral bankruptcy of immigration restrictions. The entire book is available for free download.

To look at immigration as a moral question, I checked out the Southern Baptist Convention's Ethics and Religious Liberty Commission's essay on immigration, written by Richard Land. Read the whole thing, but notice that Land contradicts himself. He defends charity extended toward illegal immigrants, writing that "(o)ur government should not criminalize private citizens who give a cup of cold water, a hot meal, a warm bed, or medical assistance to those who are in our country illegally." In his view, we should only "criminalize private citizens" who voluntarily trade with "those who are in our country illegally" and therefore help them buy "a cup of cold water, a hot meal, a warm bed, or medical assistance" for themselves.

Restrictions on international labor mobility bear an uncomfortable resemblance to restrictions on African-American migration during the nineteenth century and during the Jim Crow era. Here's a passage recounting a tragic incident from Leon Litwack's North of Slavery, pp. 69-70:

"In southern Ohio, an aroused populace forcibly thwarted an attempt to settle the 518 emancipated slaves of Virginia's John Randolph. Defending that action, an Ohio congressman warned that 'if the test must come and they must resort to force to effect their object, the banks of the Ohio...would be lined with men with muskets on their shoulders to keep off the emancipated slaves.'"