BEcause we make a mistake if we see the mexicans as being of one mind. There are individuals in the mexican army who are involved in the drug trade that can send their units out to protect a shipment or anything else they want. Anything can be done for a "small" fee. Come on, we all know this about that so-called country, it's a toilet. It's more or less anarchy. Sure there's a lot of nationalistic fervor to claim US territory (which they had held for like 20 years when we took it, so much for ancestral claims), but I don't think any of it is terribly organized.
"Anything can be done for a "small" fee. "
Yep, In San Diego they just caught two Coast Guardsmen who were waltzing illegals in the front door and out the back door into the U.S. for 3 grand apiece.
This was through the border crossing building itself.
A "Second Mexican War" ? hardly ...