In 1865, Wild Bill Hickok killed Dave Tutt in a Missouri public square in the West's first notable "walkdown." One hundred and twenty-nine years later, Bernhard Goetz shot four threatening young men in a New York subway car. Apart from gunfire, what could the two events possibly have in common? Goetz, writes Richard Maxwell Brown, was acquitted of wrongdoing in the spirit of a uniquely American view of self-defense, a view forged in frontier gunfights...