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.
While the idea of altruistic aliens is rare on the big screen, its been a staple of some of the best written science-fiction for decades. The Day the Earth Stood Still was based on a short story that appeared way back in pulp form before WW2 called Farewell to Master. Perhaps the most classic work in the sub-genre was Arthur C. Clarke's seminal 1953 novel, Childhood's End, in which a powerful race of alien Overlords drag humanity kicking and screaming into a golden age of peace and prosperity. It turns out the Overlords are hiding their real goal from us, but only so they can perform a great service for the human race. Clarke would revisit the helpful omnipotent aliens theme in 2001: A Space Odyssey.
The idea of ET coming from the sky with an armful of technological goodies and impassioned rule that solve all our problems is a familiar refrain in myth and fantasy. (Some authors took a little too seriously as in Chariots of the Gods.) It resonates in part because it's a modernized incarnation of the benevolent deities which populate human mythology and story-telling back to the dawn of history. Given empirical experience with advanced human cultures universally steamrolling over less developed ones, in the event real extraterrestrials millions of years beyond us ever drop by, we better hope they are friendly and wise, or at least indifferent. Because if they are hostile, territorial, or insanely xenophobic it will not auger well for us.
For purists like me the best science-fiction is hard science-fiction. Most of the aliens in hard sci-fi I've read lately lean to the unfriendly side. Stephen Baxter's Xeelee series is full of diverse, intelligent denizens, most of whom either don't care for humans one way or the other, or are hell bent on waging cosmic genocide. FWIW I thought Baxter's Qax were one of the coolest alien concepts ever! Peter Watts created a unique alien neurobiology in Blindsight where simply telling the ET protagonists We Come in Peace is automatically perceived as an act of war, no matter how gently or sincerely it is framed.
Channel your inner Frank Drake. Do you think there are intelligent aliens in the universe that we will ever have contact with? Will they be helpful, and if so, what should be their first order of business in solving our problems?