John Derbyshire was interviewed by the Economist, and the subject of the border came up:

[The Economist]: You have been a strong supporter of both democracy and restrictions on immigration. If it came down to it, which of these two values would you think more important for the United States? If, in a multistate referendum, the voters of Texas, New Mexico and Arizona decisively rejected building a wall between Mexico and their borders, and a group of aggrieved citizens decided to do so anyway—or decided, let's say, to patrol the border on their own, with firearms that they used often—would you support the renegades or the majority's decision?

Mr Derbyshire: It's the NATION's border, not just Texas's, New Mexico's and Arizona's. Of course I would support citizen action. Heck, I'd be down there with them. [Twelve questions for John Derbyshire | Democracy in America | Economist.com]

The point is that the Southwest's porous border is no longer just a problem for the Southwest. When Mexicans come across the border they no longer settle in the Texas but spread throughout America.

And there are people in the Southwest who aren't interested in protecting the border.

A while back, I got an SPLC email saying that

Neither the chief of Border Patrol in the Laredo sector nor Laredo’s mayor are happy that Jim Gilchrist’s Minutemen are coming to town.

A quick look at the underlying story told me that the Border Patrol agent in question was Acting Chief Patrol Agent Reynaldo Garza, his Deputy Chief was  John Cristian Esquivel, and the Mayor of Laredo was  Raul Salinas.  O-o-kay, maybe they don't like the Minutemen. But who cares?