Er, because they're the ones paying illegal immigrants to cross the border, and thus the driving force behind the problem?
Your comments about enforcement "not being your job" are certainly valid. But then again, you also have legal obligations to not break the law. The question is: how does one check the "legal" status of a person without imposing honerous overhead?
That's where the "guest worker" idea comes in. If a person is officially registered and in an official database; and that person provides you with documentation that can be verified against that database; then you have a simple "yes or no" approach to not hiring illegals. (It could also be tied in with your IRS reporting -- put these folks on the tax roles, too!)
Okay doke. Before anyone boards a bus, train, or plane, make it a taxi too; one must prove their citizenship; afterall transporting illegals is a crime. Also, I do not think people or car dealers should sell cars to illegals, they would almost certrainly be used for the same purpose.
You do not need to prove citizenship to get a contractor's license, so home owners should ascertain that the contractor they use is legit. For that matter many autoshops and restaurants are owned by illegals; patronizing these services is the same as hiring them.
The deal is these folks that advocate this type of enforcement have no problems placing burdens on businesses and large businesses usually don't mind because these burdens squeeze out little guys. That's why they call for employers to insure employees, aid in housing and to basically play daddy to their employees. I provide a quality product at a competitive price, by doing so you eat, my employees eat and the world is bettered.
And they will soon be on the voter registration rolls. Sorry, I don't want Mexicans voting for politicians who will be making rules for me. If I want to live in a corrupt hellhole I'll move to Mexico.