The current violence in Mexico is a pale shade of a real civil war/ revolution. The last Mexican Revolution lasted 10 years, killed 1.3 million Mexicans (mostly civilians) over 500 Americans, and included a raid on Columbus, NM, a significant US punitive exhibition, and a sizable cross border firefight at Nogales, AZ.
If Mexico broke out into actual civil war, we would have to put a lot of troops on the border to secure it. A wall would not cut it. Tens of millions of Mexicans would seek to come north. Not to mention the likely spillover as people on this side of the border picked sides.
The human cost would be immense, the economic damage to Mexico incalculable, the cost to the US significant and it would make Syria look like a schoolyard scuffle.
Which is precisely why in that case the only solution is US Occupation of Mexico.
The wall would go a LONG way to making the Mexicans stay and fight, rather than running across the border into the “arms” of this country. It would be far too easy to simply run across an un-walled border. Our border people would be overwhelmed at the mad rush! That is simple logic.
This is why the Bushes and the other RINOs have been fighting so hard to keep the door open - to stave off a giant Venezuela appearing next door, never mind the cost of immigration to our own citizens.
And if they do have a Revolution, it will most likely result in a full communist dictatorship like Cuba.