When a nation's security is threatened, are civil liberties at undue risk? If so, why? Consider a plausible account. In the midst of external threats, public overreactions are predictable. Simply because of fear, the public and its leaders will favor precautionary measures that do little to protect security but that compromise important forms of freedom. In American history, the internment of Japanese-Americans during World War II is perhaps the most salient example, but there are many more. Consider, for example, Abraham Lincoln's suspension of habeas corpus during the Civil War, restrictions on dissident speech during World War I, the Roosevelt Administration's imposition of martial law in Hawaii in 1941, and the Communist scares during the McCarthy period. Many people believe that some of the actions of the Bush Administration, in the aftermath of the September 11 attack, fall in the same basic category. Is it really necessary, under some sort of Precautionary Principle, to hold suspected terrorists in prison in Guantanamo? For how long? For the rest of their lives?

In explaining how public fear might produce unjustified intrusions on civil liberties, I shall emphasize two underlying sources of error: the availability heuristic and probability neglect. With an understanding of these, we are able to have a better appreciation of the sources of unsupportable intrusions on civil liberties. But there is an additional factor, one that requires a shift from psychological dynamics to political ones. In responding to security threats, government often imposes selective rather than broad restrictions on liberty.