"It's in your nature to destroy yourselves"
This line, above all the catch phrases and one liners is the one that's permanently stuck in my mind. In the short time that the T-800 is with John and Sarah, he makes that comment after observing humanity. (That's assuming the assessment didn't originate in the future, depending on what version of T2 you watch) But on opening night in the cinema, I think I was 14 at the time, that line hit hard. Humans are so basic, even a Terminator can see we're trouble.