I don't want to sound dismissive but... Well yeah.
We already know humans are dangerous. And that is humans who are conditioned to be social, and who have empathy and who rely on other humans for all sorts of things. Plus with fear of a legal system punishing them.
Now imagine a human like intelligence without empathy, that is not conditioned from childhood to be social, and that is inherently threatened by us and not reliant on us. Would you want that guy living next door?
Oh and it's 100x smarter than you.
I think all this is 100 years away, but that's the theory. Skynet doesn't have a subconscious telling it not to murder it's parents...