I agree with Ramesh Ponnuru...

...this morning (which is news in and of itself) when he writes, "New Immigration Bill Has One Terrible Flaw" (my emphasis):

The guest-worker program is where they go wrong. For the Republican politicians who have in the past been its main supporters, this provision is like a dessert with no calories: Businesses get the benefit of the temporary workers’ labor and they get to make some money, but the rest of us don’t have to make room for immigrants in our society, and Republicans don’t have to worry how they will vote.

That’s exactly what’s wrong with the idea. One of the worst things about illegal immigration is that it creates a class of people who contribute their labor to this country but aren’t full participants in it and lack the rights and responsibilities of everyone else. A guest-worker program doesn’t solve this problem. It formalizes it.