Check this out -- noted scientist Stephen Hawking believes in the certainty of intelligent alien life. Cool, huh? But... (There's always a "but"...)
"We only have to look at ourselves to see how intelligent life might develop into something we wouldn't want to meet... I imagine they might exist in massive ships... having used up all the resources from their home planet. Such advanced aliens would perhaps become nomads, looking to conquer and colonize whatever planets they can reach."
Is the prospect of alien warrior raiders chilling enough for you? No? How about this, he notes that a visit to Earth could turn out like Columbus' voyage to the New World, "which didn't turn out very well for the Native Americans."
So much for first contact.
If you think Stephen "I'm and Independence Day Fanboy" Hawking is a downer, try "Nihilist Stevie" who posits that intelligence itself may be a limiting factor on the presence of intelligent life in the cosmos, "Perhaps they all blow themselves up soon after they discover that E=MC2."
My theory is that if alien space vikings descend upon us in starship arks to denude our planet, Great Cthulhu will rouse from his slumber to swat the invaders from the sky. He will not do this out of any misplaced love for humanity, but because these pathetic insects need to be reminded how puny they are.
Ia! Ia! Cthuhlu f'taghn!