Don't beat yourself up about agreeing with a Dem. Weldon's a Republican.
I realizes that right after I posted it. If these congress-critters knew anything about sealing borders, we'd be able to keep insurgents from getting into Iraq AND the USA. Read my tagline. I am so afraid that our open borders will result in an attack that will dwarf the casualties of 9/11. All because these same folks won't take a stance.
It's not all that likely that the terrorists will use the US-Mexican border, as opposed to any of a hundred other points of entry.
Now, aliens do get across the border - but a huge percentage of them are caught and turned back at some point. It's not a sure-fire way. And if you're planning something big, and you've got money, why take a chance?
Physically sealing that border against terrorists would be hard, if not downright impossible. That's why we need to fight them and keep them tied down overseas.