From the The Charlie Rose Show, October 23, 2009, an interview with the founder of the modern state of Singapore. This link starts automatically at 3:14:
Charlie Rose: "And immigrants has [sic] been America’s strength."
Lee Kuan Yew: "Absolutely … But, mind you, immigration of the highly intelligent and highly hard-working, very hard-working people. If you get immigration from the fruit-pickers [chuckles for several seconds at the idea], you may not get very far!"
But, but ... what about the crops rotting in the fields?