James Surowiecki makes the humanitarian case for a guest worker plan:
In fact, whatever benefits the guest-worker program brought to the U.S. economy or to particular businesses, the biggest winners would be the workers themselves. The Harvard economist Dani Rodrik has calculated that the economic value to poor workers of a comprehensive temporary-work program dwarfs the value created by lowering trade barriers or eliminating capital regulations. When a good made by a foreign worker enters this country, the worker gets only a tiny slice of what we pay. But when the worker himself comes into this country his earnings can rise by a factor of ten or more. There are few, if any, foreign-aid programs that do as much for people in developing countries as simply allowing them to work in the U.S. legally. Congress, of course, is under no obligation to care about foreign workers. But the program's costs to American workers are negligible, the gains for the guest workers are enormous, and the U.S. economy will benefit.
The plan has the benefit of being a politically palatable way to jack up levels of legal immigration. There is no reason for labor participation and citizenship to be so closely aligned, especially given how many immigrants don't even aspire to the latter.