The economic argument for mass immigration has never been strong, but sadly the GOP leadership buys into all the hysterical myths.
I suspect that the standard economic argument for illegal immigrants isn't the real motivation behind letting these people flow into the country in large numbers. My guess is that the guy who runs across the border from Mexico is allowed to stay here not because he represents a source of cheap labor, but because he represents a new customer for countless numbers of businesses here in the U.S.