If the not so well off and uneducated are stuck in Mexico then Mexico knows they will have a revolution there, thus they want to send them here while they enjoy their lavish lifestyle.
The reason the US supports corrupt oligarchies everywhere on earth and especially in Mexico is because the US has been run by a cabal of corrupt oligarchs ever since Clinton bought off the Republicans with the best seats at the corruption table and the Republicans then tossed out Gingrich and DeLay to keep them from getting in Clinton's way.
That's the reason the powers that be are in a panic over Trump. He knows their game from the inside out and knows where the bodies are buried as well as where all the weak links are and also has plenty of silent friends in high and low places that know how to take help him take advantage of that knowledge.