Dangerous aliens?

Astrophysicist Hawking says that aliens exist, but meeting them may be dangerous because they "could rob the Earth of its resources." He needs not worry: Homo "Sapiens" is already seeing to it,finding also a way to pollute the environment with ecological disasters like the sunk oil rig in the Gulf of Mexico, which threatens to dwarf the Exxon Valdez disaster. Hawking's alien nomads, having seen how mankind is trating his own land,water and air, would decide to go elsewhere