If there are aliens, they will be evil.
Let me illustrate this.
An alien we’d meet would most likely to be more advanced than we are: scientifically, culturally, morally, in all the ways that cultures presumably tend to crawl upwards as they get older. We are young; the universe is old. We’re not likely to go star-hopping anytime soon; anyone that’d come to greet us would be more advanced than we are: outgrown the follies of racism, hate and war…
And evil, to our eyes.
The reason for this is that liberal, progressive, “new-fashioned” morals appear outright evil to “old-fashioned” conservative people. Someone that is against, say, equal rights to women and gays, is not likely to be an actively sneering and moustache-twirling villain, opposing the forces of light and progress. No, he (could be a she too) is against something evil. Not anything lib, but immorality; sin; degeneracy; unnatural acts; inability to see that gosh darn it things just have to be the way they are.
Let’s not say our common modern morals are the end of the road. When we grow a bit older, we’ll see reckless young idiots taking things too far, too, acting with morals that are against how things just have to be. They’ll be having sex in ways that’ll seem an utter perversion of all we old ones have fought for; they will gladly vote for oppressive laws that are a spittle-flecked anathema to us. I’m not saying their morals will be worse than ours, no, but just the opposite; it’s us that will be too set in our ways for the most part to see that they’re right.
Think about this from the perspective of a different alien: a modern improver landing in a medieval village. The improver will set to work to make the life of everyone in the village better, fuller with freedom and joy. The result? The village will be shell-shocked out of its skulls! The priests will be livid at the sacrileges; the husbands furious at the diminution of their power over their wives. The wives will be, likely as not, equally terrified by this new, outright Satanic concept of no gender roles. And voting and democracy, hell, that’d be anarchy, if our medieval village knew such a word to use as a slur. The improver could explain every individual concept, and fully and perfectly communicate them; but their whole and thus any individual part would be beyond the grasp of someone with a”whole” of morals already within. One couldn’t fit a modern round peg into a medieval moral landscape with only straight lines, and thus only square holes, in it. The rounding takes time.
Everyone in the village will be very unhappy and disturbed for a long while, for a whole generation, probably; and the improver will appear a real demon, acting in ways that are more moral than those of the village, but alien to them. Depending on the improver’s sex, he or she will appear either a rake or a whore; a glutton, a hedonist Satan, a boaster, a child with no respect and no manners; impious and a whole lot of other old slurs. Not just alien; but an evil alien.
Now, imagine an alien landing on the White House lawn, looking around, and then blasting to atoms the House, and the houses of the Senate and the House of Representatives, killing everyone inside.
Had an evil alien arrived? Would certainly seem so to us; but might just as well be the alien was genuinely morally outraged by our backward system of “politics”, and knew negotiations with it would be impossible and sure to cause nothing but worse bloodshed. Thus, a decapitation, the installation of a perfect computer central brain, and then a lot of hurt feelings when the natives fail to see how the alien was acting with their best interests in its hearts.