Hawking shows that even geniuses can say stupid things.
In this report, Hawking says contact with aliens could be risky – CTV News Stephen Hawking is quoted as saying that there are “almost certainly” intelligent alien life forms and that they may be “nomads looking to conquer and colonize”.
First, there are several compelling reasons to believe that either we are alone, or nearly alone in the universe (see the rare earth hypothesis); or, if not alone, we are one of the most advanced civilizations as physicist John Barrow argues compellingly.
Then there is the matter of the incongruity between a civilization having the powerful advanced technology such an endeavour would require and yet not having advanced in ethics beyond such violent tendencies. Such a powerful yet violent species would surely have either blown itself up or be preoccupied with killing themselves to engage in the immense cooperative enterprise required to engage in conquest across the galaxy.
Then there is the contradiction between the immense knowledge such an endeavour would require and the sheer stupidity of wasting resources on conquest rather than “terra-forming” or other methods of employing resources closer to home and thus easier to access.
So either Hawking was misquoted or is willing to make sensationalized misstatements to sell books. We he probably, or ought to have, said is that dangerous extraterrestrials cannot be conclusively ruled out, but are exceedingly unlikely.
But that wouldn’t sell too many books, or newspapers.