The events of 9/11 illustrate in tragic detail the shortcomings of a black list approach to national security. The so-called black list model seeks to identify threats before they can manifest. The drawback, of course, is it cannot possibly defend well against every foreseeable threat, and is powerless against the unanticipated.
The counterpoint to the black list is the white list approach, which owns singular authority to define and grant all permissible freedoms. By permitting only pre-approved activities, it needn’t monitor endlessly for bad behavior and provides a stiffer defense against unimagined attacks.