The problem is, once they get an amnesty, they'll find better jobs and the pork slaughterhouse slave-master is going to just hire more illegal immigrants for the same crap wages he'll no longer be legally allowed to pay his current employees, thus compounding the already dire problem we have with illegal immigration in this country.
In the 1980's Reagan passed and amnesty with the hopes that one of the benefits would be a sever slowing of Illegal immigration. It did not work then, and it will not work now.