...At the same time, we really do need to have at least some degree of positive control over who gets to cross the border and work here, which is why I think some version of the "guest worker" program, coupled with a compliance-checking/registration system on the part of employers....
I think everyone would agree with your assessment. If there is a need to for guess-workers, let's do a full study on the needs and let's "invite them" (no one is forced to) to work for a period of time, but let's make it all LEGAL. Also, the opportunity should be offered to different countries, not just Mexico.
That is a very bad idea. It is what is destroying Europe because it creates a class of citizens without full rights who will soon be agitating for full citizenship, not to mention their children who will form street gangs and welfare dependents. We should not sell out our country for cheap lettuce. There are people here who can do their work.