I think the more intelligent something becomes, the less intentional harm that organism would impose upon others.
Think about how that which has less intelligence, is always more dangerous and destructive, a universal pattern that seems to hold true with no exceptions; But I consider sociopaths as not truly sentient beings, and often below compassionate intellectuals, as true self-preservation can only be accomplished with the aid of others.
Sentient Human Computer Nerd (a non-sociopathic one) = Harmless, does not want to harm others
^
Less intelligent Football Player (brain damage) = Can snap like a gorilla and murder without good justification
^
Frat boys, constantly drinking (Additional brain damage) = Will tie an innocent person to a post and cut open their stomachs
^
Religious people = Crusades killing others ruthlessly
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Gorillas, chimpanzees = will tear people apart, literally, without torment
^
Bacteria = instinctual destruction
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Black Holes (AFAIK; most destructive force in the universe) = No intelligence/DNA whatsoever
While one may say a person can be smart and evil at the same time, this is true, as more than 10% of the human population consists of psychopaths that live and walk among us, pretending to have emotion to blend in, however, the truest danger, in my opinion, is that which has lesser intelligence. In all history no known genius has been a psychopath. As far as I know, Einstein didn't torture kittens for pleasure, and if someone goes and says hitler was smart, you're totally wrong, he was not.
My theories are not intended to hurt anyones feelings; I do believe a person can be intelligent, and religious, and often compassionate and kind, its just that which makes them dangerous is their hindered grasp on reality (due to delusions imposed by religious manipulation), and lack of strong self preservation values.
So ultimately, if we encounter intelligent, sentient (non sociopath) aliens, they will only harm humans in self defense, and probably only seek knowledge, ideas in their quest for immortality.