Noah Smith for Bloomberg, here:
"Exactly this sort of open borders immigration policy has received enthusiastic support from a dedicated core of libertarian economists, notably Bryan Caplan of George Mason University. These economists believe in relaxed immigration rules not because they want higher GDP growth, but because of principle -- they view national borders themselves as an unacceptable form of government intervention in the economy. The open borders crusaders are so zealous that moderate supporters of increased immigration, such as tech entrepreneur Vivek Wadhwa, are often the targets of their ire. University of Chicago economist John Cochrane has also voiced support for the open borders idea."
