So what is the difference? Not an outward difference, such as how they look, but fundamental differences. And a consistent difference, between humans and all aliens. It's not reason, surely. I highly doubt that it's spunk. And please don't try to convince me of that 'advanced technology' story, because I won't believe it. First, in some stories, the inhabitants of other planets are incredibly primitive. Second, who says that humans themselves won't reach the same degree of technological prowess?
Then what can the answer be? I have a theory--with an occasional exclusion, I'm sure--and it is this: we are different from the aliens of distant planets in that we can tell stories. And not merely telling facts in an enjoyable way, nor just cautionary tales of 'do this or you will die a horrible death': I mean creating stories with our own imagination. Allow me to show my evidence.
In Galaxy Quest (a favourite film of mine, starring Tim Allen), we see the Thermians, who are in desperate need of help from their all-time heroes... who just happen to be characters from a Star Trek-esque TV show. These Thermians believe the episodes of that show to be 'historical documents', because they have never heard of fiction. Deception, they know well enough, due to Sarris (the villain) using it on them constantly. But they've never heard the concept of telling a fictional story for enjoyment. This makes things very difficult for the had-been heroes of Galaxy Quest. But let's not stray into spoiler territory just yet.
The next example can be found in the cartoon show, Transformers: Rescue Bots. Specifically, the episode called "Once Upon a Time". In said episode, the Burnses and the Bots find themselves lost and separated in a forest. The catch? This forest is the home of fairies, according to local legend. Most of the characters couldn't care less about the legends, though one of these thinks it good for his own story he must write. Still, one or two of them wonder if these things--literal old wives' tales--might be true. Especially after...shall we say, certain strange happenings.
But this is just part of the picture. The main focus of the story is that of stories, stories that may or may not be true. Chase (one of the Bots) tells the humans that on their planet, they didn't have things like fairy-tales. They do, however, have stories like "The Bot Who Didn't Clean His Windshield": cautionary tales and such like. They usually end with the titular Bot being eaten by a giant space monster. Cybertron may have some of the most advanced tech in the universe, but I wouldn't want to live there if those were the only kinds of story to hear.
Which brings me back to my point. How many sci-fi stories have you found in which the aliens tell things like fairy-tales? It's usually just them telling what they believe to be facts, even when they are legends. To be sure, there are exclusions to this theory. I just can't really think of any. Even those on other planets (such as Malacandra) that tell stories in exciting or epic ways do not create the stories themselves: they tell those stories about things that truly happened. And this is storytelling too, good and important. But not the same kind.
And why does this matter, you may ask? I mean, fairy-tales are just people trying to explain things they didn't understand, or trying to force their little moral systems on other people, right? Only if you happen to be one of those modern, Politically Correct types. In the real world, they are something different entirely. And that leads me to a very important point.
In both of those examples from before, in both Galaxy Quest and Rescue Bots, those fictional fairy-tales... come true. In the first example, those had-been heroes from a Star Trek show are summoned by an alien people--who believe these actors to really be their characters from the show--to help defeat a space villain. As this is a comedy, in both senses, you can be assured that they save the day. I won't say how they manage to do this, but I will say that, the moment the Thermians find the stories of the Galaxy Quest heroes to be lies, they turn round to see the stories come true for the first time. And the heroes of the movie become the heroes they had before only pretended to be.
In the second example, the Burnses and Bots get lost and separated in a forest while trying to understand why its trees are falling over. They unwittingly act out several familiar tales, which you may recognize when you watch it yourself. In that way, the fairy-tales do come true, as well as in another, smaller way, but no less important. A way very similar to what they did in "The Haunting of Griffin Rock". Put quite simply, it seems anything can happen in Griffin Rock.
I've found that people love disproving magic and fairy-tales. I personally have mainly only come across it in movies and TV shows, and such like. People in those say things like 'magic's only science we haven't figured out yet', or 'there are no such things as that!' Sometimes they're disproved, sometimes not. In Sherlock, in a great many kid's shows, all kinds of things. I've found few things that aren't specifically fantasies that include real fairy-tales and legends.
And oftentimes, folks like disproving heroes in general, showing that they aren't really great, and are just lying to you and everybody. Sometimes this goes hand-in-hand with disproving the idea of villains, showing that they aren't really bad, and are just misunderstood victims of the heroes. These things are themes running through today's culture.
And this is why we must not lose what makes us different. Aristotle tells us that what makes us different and unique in regards to animals is our reason, our logic, rational thought. This is something we cannot lose, not without losing all humanity within us. But what makes us different from those of other planets?
You know this by now, right?
It is our ability to tell fairy-tales. To create something in our own minds, to do "such noble feats as bringing forth new worlds, stories, and adventures", to weave words into an image for those who will hear it. It is to reveal an eternal truth in something that may not be true, to create characters that strive for goodness even in situations that are not, to inspire hearts for beauty. To kindle a light in the eyes of the hearers, whether they be our families, our friends, or complete strangers. Or even those who have never yet heard of the tales of Faerie: those of far-flung worlds?