UAPs and the Alien Question

What’s the strongest reason(s) not to believe there’s a reasonable chance that some of the seemingly less explicable UAP sightings could be an artifact of alien life? I think the general consensus around here tends to be very skeptical, with Admin taking a dim view on the significance of some new UAP footage recently coming to light (which I admittedly haven’t looked at much myself). On the other hand, I’ve seen Robin Hanson, for instance, show a lot more credulity.

My priors on this sort of thing being real aren’t especially low but nor are they especially high. One of the strongest arguments against seems to be that alien life, or some silicon spin-off therefrom, would be expansive and remake the galaxy or local group in whatever way it sees fit, which should preclude us from existing in the first place. I can’t say that I’m confident enough that I’m not missing something here to put too much weight on this though. I also read the Jim’s Blog post laying out the case for the uniqueness of our local group, and of our solar system in particular,

https://blog.reaction.la/science/it-is-the-will-of-gnon-that-we-shall-fill-the-stars-and-subdue-them/

but this too seems less than definitive.

Should these arguments alone be sufficient reason to dismiss the possibility of UAPs being an artifact of alien life? Are there other stronger reasons to do so?

It's pretty simple.

First, even if we assume that there is technologically advanced life elsewhere in the galaxy (reasonable IMO), the lightspeed barrier makes the prior probability of visitation extremely low. Interstellar travel would just be an incredibly slow and high-effort thing in the vast majority of cases.

Second, suppose that, however highly improbably, aliens have come to our solar system. Maybe they have a small base on a moon of Jupiter or wherever. Periodically, they send one or more ships to Earth to check us out. What would we expect that to look like? Nothing like the actual UAP reports we get, I submit. I mean, where are the damn ships? Why can't we actually see them for real? Why these fleeting glimpses, but absolutely nothing before or after?

Obviously, you can tell just-so stories to explain the phenomenology. Ultra-advanced cloaking technology, whatever. But now you're just arbitrarily positing magic as your explanation. A far more probable and parsimonious explanation is that UAPs are socially and psychologically generated phenomena, much like cryptids or angelic / demonic visitations.