In the first few weeks after the September 11, 2001, terrorist attacks on America, a dominant view in America was that some restrictions on civil liberties would be necessary to help prevent future terrorist attacks. For example, law enforcement authorities might need greater freedom to search and detain suspicious individuals. In discussing the effect of these security measures on civil liberties, the metaphor of a balancing act soon emerged. For example, columnist Murray B. Light of the Buffalo News wrote, “The nation needs to carefully balance its security concerns with its heritage of civil rights for all.”

Light issued that warning in a column advocating the preservation of civil liberties. But the theme of balance has also been taken up by those who feel that some curtailments of freedom are justified. As University of Chicago law professor...