From Barack Obama to Karl Rove, the ruling class is in unison: The NSA’s collection of data on virtually all Americans is essential to preventing you from “being blown to smithereens on your morning commute” – as the Wall Street Journal editorial put it. In the words of General Keith Alexander, director of NSA, this surveillance has “helped to prevent” “dozens of terrorist events.” Later, the tally rose to “over fifty.” Project Constant Informant, which tracks essentially all American phone calls, allows matching the account holder’s identity with each call’s precise location in time and place. Another, PRISM, gives access...