I'd also doubt the assumption that democratic alien civilisations would be likely to be friendly and peaceful towards Earth if we ever make contact. Democracies aren't automatically peaceful; in fact, in the appropriate conditions, a democracy can become an irrational mob baying for the blood of real or imagined enemies. If enough of the alien populace was persuaded (by a pliant media or an influential orator, or some equivalents thereof) that Earth posed a threat, I suspect they'd be likely to vote to asteroid-bomb us out of existence before we do the same to them.
Of course, how alien psychology and decision-making (including perception of risks, aggression, altruism and such) would work would depend on the evolutionary conditions that shaped their neurology, much as human psychology depends on the hunter-gatherer condition.
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