If these psychos are going to try to get weapons of mass destruction into the U.S., they're not going to bring them in through the checkpoints. They're going to smuggle these weapons over the border in some remote location from Canada or Mexico under the cover of darkness. They're going to use the same tactics that they use to get large quantities of drugs and illegals into the country.
Let's at least try it. What do we have to lose by trying? The troops can always be removed, if it doesn't work.