Intuitively, that seems to make sense on the superficies, and it appeals to the natural human desire to be more broad-minded than average. Nonetheless, it’s a view that doesn’t hold water under scrutiny.

We’ve explored the Solar system well enough to be pretty sure there isn’t any macroscopic life that we can recognize in the system, except right here on Earth. There are no green Martians with antennae, no hidden civilization just below the cloud layer on Venus, no great trading cities on the moons of Jupiter, etc. — certainly nothing capable of interplanetary flight. Multiple independent nations have sent probes to all the major planets and most of the larger asteroids and turned up no evidence of anything large enough to see without an electron microscope. *Thousands* of independent amateur astronomers are constantly looking at the various planets and asteroids, to the extent that, when some obviously natural phenomenon occurs on one of them (like, the recent meteor impact on Jupiter), there are always several different amateur videos of it that you can find on YouTube. If they were launching interplanetary spacecraft, that would be spotted too.

That leaves the rest of the universe, but even if there were life in other star systems, indeed, even if we assume that *most* other star systems have intelligent life (a rather dubious proposition), there’s no reason to suppose any of it would find its way here. Interstellar flight is inherently a more difficult problem than most people realize. It’s possible there’s something very fundamental we’ve misunderstood about the physics of space-time, but it would have to be quite major to allow for practical travel to other star systems on a timeframe shorter than decades per trip to the very closest systems, MUCH longer for anything distant. Scientifically speaking, unless somebody figures out how Einstein’s cosmology is WAY OFF (much further off than Newton’s, more on the order of how wrong Aristotle was about everything), the most reasonable conclusion at this time is that nobody, at any technological level, can transport matter across space at more than a fraction of the speed of light.

At available speeds, then, every system you travel to is an extremely major undertaking, even for a society overwhelmingly more technologically advanced than ours. There couldn’t possibly be ships coming and going often enough to add up to multiple UFO sightings per generation. One alien ship sighting every few centuries is vaguely imaginable, but it would have to be a ship large enough to support the crew for years at a time without resupply, so there’s absolutely no way it could be kept secret if it actually entered Earth orbit, much less landed. Dozens of interstellar ships in our atmosphere per decade is flatly impossible even if you assume they could stay secret because they’re invisible, inaudible, and undetectable on radar.

I suppose pure-energy beings with no physical body could maybe zip around at faster speeds, and thus could visit more often, but if so they wouldn’t be using spacecraft to do it, so rather than UFO sightings you’d be looking for ghost stories or something.