The assumption in these border control things is that the danger is going to be from people coming in from abroad, or who at any rate look foreign.

You just need to think a litle about that, and it becomes clear that it is a very silly assumption.

In England currently there's a big worry about a bunch of young British muslims who have been picked up in connection with alleagations they were preparing for a bombing campaign.

Anf over in the USA in Texas a couple of very mainstream respectable looking white Texans are waiting sentence for possession of a horrifying terror arsenal:   

Inside the home and storage facilities of William Krar, investigators found a sodium-cyanide bomb capable of killing thousands, more than a hundred explosives, half a million rounds of ammunition, dozens of illegal weapons, and a mound of white-supremacist and antigovernment literature.

Here is a story about the case from an American paper, and another from an English paper.

"Critics say the case shows that the authorities, obsessed with Islamic terrorists, have ignored the deadly assortment of domestic extremists. America's right-wing groups, though diminished in numbers since 1995, have become bent on acquiring weapons capable of mass slaughter."