The U.S. of A. can only be conquered from within,and I fear it has been.
Not the only reason, easy low interest college loans have convinced many of our students that working to make college payments is beneath them. This was not the case when I was in college; crop harvest was a great way to make extra money without a long confusing interview and hiring process.
I still favor a testing service on the border to allow anyone capable of passing a high school sophmore level math and English test and giving them a temporary resident card (with working privileges). In this way we would encourage better education in Mexico and ensure that our immigrants were the cream of the crop so to speak. Of course Mexico would halt border crossing in a heartbeat once they realize what we are doing.