What's Halloween without a posse of gun-toting cowboys or those gory rubber costumes heavy on the fake blood and guts?... "Halloween is a beautiful target," said Douglas Raybeck, a Hamilton College anthropologist. 'People dress up as the devil and all these dark characters and you associate with demons.... You add in the recent tragedies and people become extremely sensitive to this sort of thing."... The schools "don't want to be seen as promoting violence or condoning it," agreed Dr. Richard Wessler, head of Pace University's psychology department. "Even costumes too gory could send the wrong message."