SAN FRANCISCO - John Gilmore's splendid isolation began July 4, 2002, when, with defiance aforethought, he strolled to the Southwest Airlines counter at Oakland Airport and presented his ticket. The gate agent asked for his ID. Gilmore asked her why. It is the law, she said. Gilmore asked to see the law. Nobody could produce a copy. To date, nobody has. The regulation that mandates ID at airports is "Sensitive Security Information." The law, as it turns out, is unavailable for inspection. What started out as a weekend trip to Washington became a crawl through the courts in search...