In seeking to evaluate the efficacy of post-9/11 homeland security expenses--which have risen by more than a trillion dollars, not including war costs--the common query has been, "Are we safer?" This, however, is the wrong question. Of course we are "safer"--the posting of a single security guard at one building's entrance enhances safety. The correct question is, "Are any gains in security worth the funds expended?" In this engaging, readable...