On film most sci-fi aliens are up to no good, and during the B-movie heyday quite a few had a perverse taste for interspecies sex with nubile earth woman. But in 1951 a deeper plot appeared on the silver screen: Klaatu arrived in his gunmetal gray flying saucer to save us from ourselves. Naturally, we panicked and mortally wounded Klaatu, but he was still able to explain that earth, like all civilized planets, was now under new management in the form of his robot sidekicks:

At the first sign of violence they act automatically against the aggressor. And the penalty for provoking their action is too terrible to risk. The result is that we live in peace, without arms or armies, secure in the knowledge that we are free from aggression and war -- free to pursue more profitable enterprises. We do not pretend to have achieved perfection, but we do have a system, and it works. I came here to give you the facts. Your choice is simple. Join us and live in peace. Or pursue your present course and face obliteration.

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