Dan Drezner comments more thoroughly:
2) Carried to its logical extreme, isn't Hawking making an argument for rapidly exhausting our natural resources? If Hawking is correct, then the sooner we run out of whatever might be valuable to aliens, the less interest we are to them. Of course, this does beg the question of which resources aliens would consider to be valuable. If aliens crave either sea water or bulls**t, then the human race as we know it is seriously screwed.