This past weekend, the renowned astrophysicist Stephen Hawking joined what seems to be a growing chorus of cautious naysayers—or nervous nellies?—when it comes to possible contact with intelligent aliens from other worlds. He warned viewers of his Discovery Channel program that contact would be unwise, because the aliens might be seeking new resources and could prove hostile, the way Europeans were to the natives of the New World.
But notwithstanding the fact that intelligent life appears to be extremely rare, what are the odds that space aliens would really want something from our planet?
A species that masters the difficulty of space travel would certainly seem to have the brain power to mine its own resources without having to travel tens of light years (at least) to ravage our home. If Mars had dense forests of mahogany trees and bountiful oceans of bluefin tuna, would it really be worth the expense to mount an expedition just to raze and fish the planet? Even the most environmentally insensitive among us would have to concede that the hundreds of billions of dollars needed just for a round-trip to Mars could be better spent to, say, develop the technology to harvest trees sustainably or to cultivate bluefin tuna on farm.
The resource on Earth would have to be compelling and unique, like unobtainium on Pandora in the movie Avatar. And even then, the bad humans were not really out to destroy the Na'vi, who were in the way.
Earth as a nice place to colonize is perhaps the strongest argument for hostile aliens, and that's not a very strong argument. The odds that Earth's biosphere safely matches that of the alien's home planet is low. (Remember what happened in H.G. Wells's War of the Worlds?) And I'll lean on the economic argument again and say that managing your home world is more cost-effective than finding a new one.
Considering the vast distances of interstellar flight, a space-faring species not only would have to have advanced technology, but they also must have managed to avoid destroying themselves, as technological civilizations are capable of doing. Aggressive, colonizing species would likely have wiped themselves out long before getting near our neighborhood. This standard SETI argument, reiterated here by Jill Tarter, director of the SETI Institute, in response to Hawking's comments, still sounds pretty convincing to me.
By the way, if you want to know what first-contact missions are really like, and how dangerous they can be, read "A Prime Directive for the Last Americans" or the accompanying Q&A with Sydney Possuelo, the Brazilian researcher who made contact with indigenous Amazonian tribes living a hidden, stone-age existence.
Image: Amateur-made portrait of Na'vi. Harry Nguyen/Wiki Commons