Remaining on alert against terrorism is a demand of the times. There are enough people with a distorted sense of justice, for whom violence has become a way of life, to justify extraordinary prevention measures.
Greater physical security in public buildings and airports, enhanced intelligence gathering, closer scrutiny of those crossing borders - all have a reasonable place.
But there are limits. Vigilance against terrorism can't be allowed to erode fundamental tenets of democracy and fairness. Americans have only to remember past security excesses, such as the "red baiting" of the 1950s, to recognize the dangers.
The limits have been violated, recently, by ill-conceived laws that allow the federal government to detain legal immigrants without giving any specific reasons for their detention. "Secret" evidence, perhaps allegations of terrorist connections by obscure acquaintances or even an estranged spouse, can put someone behind bars for months, even years.
True, the individuals affected are not American citizens, but they are legal residents subject to the American justice system. …