"EVERYONE LOVES A GOOD TRAIN WRECK: WHY WE CAN'T LOOK AWAY." By Eric G. Wilson. Sarah Crichton Books/Farrar, Straus & Giroux. $22.Morbid curiosity. Rubbernecking. Schadenfreude. From our national obsession with celebrity crackups to the popularity of gore fests such as "The Passion of the Christ" and "Texas Chainsaw Massacre," Americans lead the world in the urge to wallow in everything grotesque, blood-spattered and shocking --as long as it's happening to somebody else.