Contagion is an apt metaphor here. Songs, ideas, fashions, commercial slogans, and urban legends are all examples of memes. It's clear from the kidney theft story that a meme need not be true to be fit for survival. One such trait is its ability, like a good ghost story, to evoke a tingle of fear in its hearer. And, on the darker side, there's undeniably a sense of power to be had by provoking fear in others.
Some people take a perverse pleasure in it.
Someone initiated that cavalcade of faxes, email and phone calls earlier this year, causing panic among travelers to New Orleans. It's hard to imagine what the hoaxer's motivation was, if it wasn't to spread a climate of fear. In succeeding, he or she induced others to do the same. An epidemic was born. The most effective antidote was, and is, true information.