The Viacom heads at MTV know that Kerry is not the only candidate this election and that's what scares them. Ralph Nader, the Green Party, the Socialist Party, the Communist Party, the Worker's World Party, and the Socialist Worker's Party all threaten the Democrat vote.
Even without the Greens, Albert Gore Junior could have won Florida in 2000 if he had only gotten all of the declared commie/socialist vote (look at the numbers sometime).