Because nuclear energy wasn't scary enough yet

"Three and a half years after the Sept. 11, 2001, attacks, the government has failed to address the risk that a passenger plane flying at high speed could be deliberately crashed into a commercial nuclear plant, setting off fires and dispersing large amounts of radiation, a long-awaited report by the National Academy of Sciences has concluded." (WP)

But fear not--"We do believe that the possibility of a successful attack using commercial aircraft is very small," says the Nuclear Regulatory Commission. Hmm. As small, or smaller than the possibility of a successful attack on a New York skyscraper using commercial aircraft?

How 'bout this one--we phase out nuclear energy, and not only do we not have to deal with Blinky the three-eyed fish, but the terrorists have one less thing to fly a plane at.