If illegals and their cheap labor are taken out of the equation, many, many businesses will begin to rebel in desperation merely to try to stay viable. The federal government eats a massive amount of our GNP. The other levels of governemnt, which are peopled by members of the same two parties who want to move up to the federal level, imitate the feds in writing worthless legislation and regulation and taxing everything imaginable.
That's why I think politicians are going to try to keep the flow of illegals going no matter what we say about it. They have also seen the side benefit of having a new constituency who won't talk back and who will vote for whoever offers the most cookies.
I think our politicians in both major parties have observed the great deal they believe politicians in Mexico get. Most Mexican politicians end up extremely wealthy from the bribe money and one party managed to stay in power over 70 years. Bringing these same voters over here makes sense if that's what you're after.