Why do people think aliens can't exist?

[ChordInversion]

I always find it interesting when people assume hyper intelligent beings would behave as we did when we discovered people and cultures we deemed (always incorrectly) to be less advanced. Perhaps we behaved that way because we're all a bunch of idiots.

Perhaps. But it's also interesting that your mind goes to humans when I noted aliens might wipe us out for our resources or because our nature as they observe it makes us repulsive and even threatening. They might well be correct and noble, with thousands or even millions years of experience showing that Roddenberry was wrong, Prime Directives are for suckers, and when species like us aren't wiped out, they soon come to wipe out others.

The assumption that we would be viewed as a 'people' or a 'culture' rather than as ants or termites or cattle is just as interesting. How do we know that what to us are sure signs of high culture would be viewed as anything but primitive (and even threatening) noise? Assumptions of high-mindedness are just as baseless as projections of 15th century human ethics onto aliens (which I agree would be a mistake). Meanwhile, the notion of competition and predator/prey may evoke images of colonial times, but they're in no way limited to humans. Contention for resources, starving out the competition, is the reality up and down the tree of life, including within species, and it is the mechanism by which an enormous amount of animal ecology has played out over the course of millions of years. I've worked with zoologists and conservation scientists who have told me some frankly gross realities. The ecological harmony we observe is the result of kill or be killed worked out over vast amounts of time, and it still has some dark even intra-species stuff baked into it.

I agree with this. Meaning and purpose are always self defined, even by those who outsource their worldviews to already established ones, which are all of them.

Self-defined, and also...impossible to ever know if you ever get it 'right,' should one grant that 'right' is even a thing.