Why would they need to be replaced immediately? It's not like they'd be going anywhere in a hurry.
To put the question another way: Say we institute a guest-worker program that's available only to foreigners applying in their home countries. Would that make things any worse for employers than they currently are? If so, how?
If we want to control the borders, they should be going fast. As long as we accept illegal workers, they will continue to come.
To put the question another way: Say we institute a guest-worker program that's available only to foreigners applying in their home countries. Would that make things any worse for employers than they currently are? If so, how?
It takes time to process those applications. Probably months. What would the employers do in the meantime? I agree that employers should only get future hires from a legal guest worker program, but until there is one, the employers will just ignore the status of their workers.