Dear Editor: School shootings are the most tragic aspect of contemporary American life. Media accounts invariably focus on the motive, as if the shooting could be rationalized or made understandable. I regard this pernicious and cowardly. There is nothing interesting or helpful about the motive for violence of this nature. Face it: In any given case the shooter was angry or depressed. They had been slighted or humiliated at the site of the murders, perhaps repeatedly. They were isolated or secretive.