Rayguns, Space germs, and Titanium

Even in our own envisioning of encounters with an alien race, we dont perceive them as pleasant.

Assuming that space-faring aliens exist, and that they are anything like us, Steven Hawking is probably correct.

Though it was posited even in Hawking's own "A Brief History of Time" that in order to develop a space faring, interstellar civilization, any alien race would have to be peaceful enough to have not destroyed themselves or their planet before acquiring space travel.

That thought kind of glosses over the fact that space technology is closely linked to military technology on our planet. Again, we tend to envision our own forays into space as military in nature. A species need not be beneficent in order to develop technology, even if the bar is particularly high for the entry into rocket science. That society just has to be pretty large and have access to plenty of resources. Like the U.S., U.S.S.R. and now China and India.

The cold war is a particularly good example for a caviat to the above proposed rule. Sure a society has to be peaceful enough not to destroy itself with the technology that leads up to space travel but that thought is only meaningful with reference to our own history. Sure nuclear power arose in society around the same time as space travel. Space travel developed as a means to deliver nuclear explosives. And that competition produced rapid advancement of the two technologies such that both advanced cultures would have been destroyed if either was warlike enough to use that technology. But then the threshold of "peacefulness" is pretty low.

Not to mention it assumes a parallel history and a culture built around out-group antagonism.

A bunch of real scientists have similar but more intelligent things to say.