This seems like a bad take. If aliens can traverse lightspeed distances with sufficient ease to stop here, it seems trivial they'd also be able to analyse comparatively primitive sensor technology and navigate out of range to avoid identification.
So to address this, I need to take a detour for a second.
Let's suppose there are two competing theories to explain the cause of the seasons. To the ancient Greeks, spring and summer signified the six months when Persephone returned from the Underworld, and her mother Demeter made the Earth bloom and grow bountiful after her absence. When Persephone left the company of the gods and returned to the Underworld, Demeter’s loss was expressed in the barrenness of autumn and winter.
Another theory is that Earth's axial tilt causes the seasons.
Now try to come at this for a second pretending you don't know the answer. Each accounts for the observations in different ways.
But the former is a malleable theory. Not because it's wrong--but because it's very malleable. For instance, the Greeks may not have known that the seasons are reversed between northern and southern hemispheres. If they observed this though, they wouldn't need to discard the theory. They can simply modify it to suit the new observation (perhaps Demeter visits the Southern hemisphere for six months and the northern hemisphere the other six).
In contrast, the Earth's tilt theory is strong. It accounts for the reason the seasons are different in the hemispheres. It explains why the sun's angle changes each day. It explains why the days get short in the winter.
If any single one of those observations were different, the theory would have to be discarded. It's a very fragile theory not because it's correct--but because if any of those observations were different, the theory would have to be discarded.
Now I think you know where I am going with this. The problem with the alien theory is exactly the same problem with Persephone. Any observation can be explained away or even taken as further proof. The theory is malleable. If the UFOs appear on RADAR, then it's proof they exist. If they don't appear on RADAR, it just shows they must be using alien technology to conceal. If they are in photos it's because they exist. If there are lack of photos, it's because they have invisibility technology. If they are only in blurry photos, it's because they only go where cameras are blurry, etc. That is, there really isn't any observation which can disprove them.
Consider also that there is nothing alien about the theory. Why can't they be angels? Or ghosts? I could easily replace every instance of 'alien' with 'ghost' and nothing would change.
(I first heard this distinction between fragile and malleable theories from Michael Shermer, though I cannot find a reference right now.)
The problem is they have been tracked on radar, multiple times and even the same event independently on different radar as well as other instrumentation. Doesn't prove Greek Gods, but possibly not Earth's tilt in this case.
