The myth persists because: 1) Those who didn't go to Vietnam--that being most of us--don't dare contradict the "experience" of those who did; 2) the story helps maintain the perfect sense of shame many of us feel about the way we ignored our Vietvets; 3) the press keeps the story in play by uncritically repeating it, as the Times and U.S. News did; and 4) because any fool with 33 cents and the gumption to repeat the myth in his letter to the editor can keep it in circulation. Most recent mentions of the spitting protester in Nexis are of this variety.
As press crimes go, the myth of the spitting protester ain't even a misdemeanor. Reporters can't be expected to fact-check every quotation. But it does teach us a journalistic lesson: Never lend somebody a sympathetic ear just because he's sympathetic.