I don't know, for some reason I think alien species would be more similar to us than a lot of people expect. For one, they would have had to have evolved in a manner at least somewhat similar to us, and that would bring about commonalities. Our views on morality (and many of our worldviews in general) are shaped in large part by our evolutionary history, and an environment that could produce an intelligent species would not be so different from our own as to produce a completely different way of thinking. We might share basic ideas like fairness, blame, reciprocation, or retaliation, for example (reciprocal altruism for instance has evolved in a ton of species of earth - if it's evolutionarily stable here, why couldn't it be there?). An understanding of causality, that events have causes and can be predicted and controlled, would certainly be present in any intelligent alien species. I'm sure there'd be others as well.
More importantly, though, any species advanced enough to travel through the stars our detect our presence in some way would have to be civilized - I use both senses of the word here. Obviously they'd have had to have built some kind of civilization in order to have created their technology. But the root word of civilization is civil, and the fact that they can cooperate enough to form a functioning society would imply a great deal about their psychological make up. For one, it would mean that they are, if not completely peaceful, at least capable of peace and understand the concept of peace. They'd have other things too, probably: a concept of fairness, some understanding of logic, and maybe an ability to suppress urges in anticipation of greater reward later. After all, it's difficult to imagine a society evolving without these kinds of traits present. Now granted, there would be differences between our civilization and an alien one, maybe large ones. My point is: technology requires civilization, and civilization requires civility to some degree. Moreover, there are bound to be certain universal characteristics (things mentioned like logic, fairness, patience, etc) that are simply required for the formation of a society. That is, any species that didn't have such characteristics simply wouldn't form a society. Therefore, we'd have to share at least some things in common with an advanced alien species. Maybe more than we'd think. Could such species still be dangerous to us? Of course. They could be internally peaceful but violently xenophobic. They could be desperate for resources. Any number of possibilities. But I think if we could sit down and talk with them, we might be surprised at how many viewpoints we share.
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