The main reason Mexico pushes for open borders on their north is that the Mexicans who go north are earning money and sending it back home. It is that flow of money Trump wants to tax to build the wall, according to his earlier statements.
The second reason is the drug distribution and production network into the US needs foot soldiers and workers.
The cash flow to Mexico is huge, especially when you figure in the drug profits. Getting rid of “undesirables” is just a little icing on the cake.
I think in the period before NAFTA...it made sense to have the easy-access border situation, and unemployed Mexicans simply crossed the border with no paperwork or visa.
After NAFTA, I think things shifted, and the younger generation Mexicans who picked up a trade or craft...suddenly found jobs for the middle-class (paying a lot less than in the US) in Mexico.
So what you have in this era...are the Mexicans without any skills (the bottom of the barrel), and to a greater extent....Hondurans, Salvadorans and Guatemalans who have replaced the bulk of the cross-over crowd.
But here’s the thing that almost no one talks about. With this smuggling route figured out...if you lived in Asia, or Middle East, or Africa....all you need to do is find some method of getting to Honduras, and then use the same smuggling route. Whether anyone wants to admit it or not....long-term, there’s a bigger problem brewing.