I don't think you can argue with this, but Hawking has also warned about any such contact with these aliens.
He said on his "Into the Universe With Stephen Hawking" television programme, "If aliens visit us, the outcome would be much as when Columbus landed in America, which didn't turn out well for the native Americans."
The inference being that Native Americans experienced disease, death and displacement as European then American invaders fought them, seized their land and forced them onto reservations, sometimes after death marches.
Hawking therefore feels that, rather than try to establish contact, humans should try to avoid contact with alien life forms.
Perhaps this is also the thinking behind most governments on Earth as they try to cover up and hide any UFO sightings and stories of aliens.
There are differing views from Jill Tarter the retiring director of the SETI Institute (Search for Extraterrestrial Intelligence) about the effect aliens may have on Earth. She is quoted as saying:
"While Sir Stephen Hawking warned that alien life might try to conquer or colonize Earth, I respectfully disagree. If aliens were able to visit Earth that would mean they would have technological capabilities sophisticated enough not to need slaves, food or other planets. If aliens were to come here it would be simply to explore."
"Extraterrestrial life with enough intelligence to travel light-years through the Milky Way already would be kinder and gentler with no need to pirate resources or use Earth as an outpost."
She went on to add, "Stephen has a brilliant mind, but he doesn't have expertise in extraterrestrial intelligence. Aliens coming here hell-bent on trashing the neighborhood and claiming all our resources - I'm skeptical of that."
But, of course, Jill Tarter doesn't have any real expertise either in extraterrestrial intelligence as she has said, regarding SETI, "Certainly, we don't see evidence of intelligent life. The case is still open. "
"The SETI Institute, in operation for 28 years and now with 150 scientists, has yet to receive one signal from intelligent beings elsewhere," she said. "Nor is there solid evidence that basic life forms - bacteria or microbes, for example - exist out in the solar system or beyond."
It would, I suppose, be preferable if Jill Tarter's opinion was accurate and that any visiting aliens would not wish us harm. But we can't be sure of this.
OTHER ALIEN POSTS:
UFO And Alien Sexual Encounters
Paralysed By The Aliens Of The Lavender Field