This is precisely why the Mexican authorities encourage this sort of illegal emigration. It is a pressure relief valve that if not there probably would result in a bloody revolution and they getting unceremoniously driven from power and probably shot. Not to mention, it brings billions of $ into their basket case of a country.
Why we support it is another matter; mainly cheap labor, a totally incompetent INS, Political Correctness run amok, political votes and voting blocs few in either Party who has to run for election want to offend. After all, if all the politicians offend those who object to this craven and illegal practice, it's a "draw" and no politician loses on that score.
The only people who lose are the non-politician Americans who feel our heritage and country is worth more than pandering for a win in the next election. We are having our country sold out for a mess of election pottage!