I think the government of Mexico really likes getting millions of military age, angry, poor mestizos out of the country so they don't have a revolt and lose their heads. If they wind up causing a revolt here, so much the better. Also, the mexican military and government are up to their eyeballs in the drug trade, so these military incursions can be expected to continue as long as we allow.
Our only hope is that evil always overreaches and someday they will wake us up to the enemy nature of our relationship with Meh-hee-coh.
" If they wind up causing a revolt here, so much the better."
Nope, counter to your first statement - If they cause trouble they might get kicked back, and Mexico loses the Billion$ that gets sent back every year.
... and even if you are correct about the Mex government being in the drug trade, just why would they want to cause trouble ? Drug dealers like nice quiet closet junkies. No muss, no fuss