My explanation of the Mexican position is that the people in charge of Mexico have a choice of ways to give basic benefits to its poorer citizens: raise taxes and provide basic subsistance or facilitate their "migration" to the U.S. so the American taxpayer can foot the bill instead.
Last time I was in Acapulco a local told me that Mexico is a very rich country but very corrupt. He said Cancun was developed by the Mexican government but is owned by a former Mexican president and his friends. He also said they pay more for Mexican gas in Mexico than the companies sell it for to other countries. So it sounds to me as though the people pulling the strings in Mexico don't want to give up a good thing. If it weren't for the escape valve we have become Mexico might end up with a revolution.
USo it sounds to me as though the people pulling the strings in Mexico don't want to give up a good thing. Yep, the European class running Mexico is corrupt and greedy, and racist as well. Even the Pope publicly stated their ethnic cleansing of the Mestizo Indians by encouraging them to leave was unacceptable.
It's time to put our foot down and make them fix their own problems, the sooner the better.