I suppose there's symbolism and allegory built into all movies, but it's clearly the rule and not the exception when it comes to science fiction. The Cold War era was rife with flicks about strange invaders taking over our way of life, or simply vaporizing us back to the stone age. Now, in a post-9/11 world, our fears have changed, and science fiction will change in order to reflect that. The Christian Science Monitor has an interesting piece on the history of science fiction as a reflection of the zeitgeist, and centers on Spielberg's adaptation of War of the Worlds as the first movie driven by a new kind of mindset that was instilled in all of us after September, 2001. Interesting reading.