[First aside: I just watched this series' exposition on the Big Bang, and it was excellent, especially with a level of graphics I've never seen elsewhere. I recommend it.]
"If aliens ever visit us, I think the outcome would be much as when Christopher Columbus first landed in America, which didn't turn out very well for the Native Americans," he said.I suspect Hawking is almost certainly right. Because, if said aliens are "moral" or if they are not, both positions have important consequences.
If they are "moral" like we (humans) think we are moral, then heaven help us. Despite any big talk, the brutal fact is that we humans have no empathy for any species other than ourselves. (Gary Francoine excepted.) Humans will kill anything -- including other humans -- it if serves their immediate needs.
Hell, we won't even save our own genetic progeny. How fucked up is a species that won't even save itself?
Very fucked up.
If the aliens are advanced enough to demonstrate some true morality and respect for life, then they will either come here and look upon us as essentially worms (in which case we're toast) or will just leave us alone and never come here at all (the "Prime Directive") point of view. In which case we have no idea any aliens are out there anyway.
The chances that they come here with about the same level of morality we have are slim, since we can't get anywhere else right now and frankly it's not clear that we're going to last another 100-200 yrs.