legalizing them is not the answer. It is a reward and an incentive to lawbreakers. If they insist on a reward for their hard labor - well, that's what wages are for. If they feel undercompensated or discriminated against, they can go back to Mexico and try their luck there.
A guest worker program would only create a demand for new illegals, since the guest workers would command a higher wage and greater protections and benefits. What it boils down to is that a "true" illegal would be more marketable than a worker who signs up for and who is under the restrictions of the guest worker program.
Bingo. Yet another reason why this plan is insane and will do nothing to allievate the situation. MAYBE if the govt cracked down on businesses who hire illegals a guest worker might, MIGHT have you, have a chance at success. But the market will always go for the cheapest alternative.