The case against visits by aliens:
1. Alien sightings remain relatively rare.
Let’s say alien drone probes can make it here. That would imply the existence of a very advanced civilization that can span great distances and command energy with remarkable efficiency. If that’s the case, why isn’t the sky full of aliens? Why aren’t there sightings from more than just military craft?
So the question is not so much, “Why don’t we see aliens?” as, “Why don’t we see more of them?” It is a perfectly valid (and embarrassing) question. On one hand, the aliens are impressive enough to send craft here. On the other, they seem constrained by scarcity.
Are we humans like those bears filmed in the Richard Attenborough nature programs, worthy of periodic visits from drone cameras but otherwise of little interest? The reality is that bears, and indeed most other animals, see humans quite often…
3. The alien-origin hypothesis relies too much on the “argument from elimination.”
The argument from elimination is a common rhetorical tactic, but it can lead you astray. You start by listing what you think are all the possibilities and rule them out one by one: Not the Russians, not sensor error, and so on — until the only conclusion left is that they are alien visitors. As Arthur Conan Doyle’s Sherlock Holmes once said: “When you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth.”
The argument from elimination works fine when there is a fixed set of possibilities, such as the murder suspects on a train. The argument is more dangerous when the menu of options is unclear in the first place. Proponents of the alien origin view spend too much time knocking down other hypotheses and not enough time making the case for the presence of aliens.
There is an argument that is often used against the alien-origin hypothesis, but in fact can be turned either way: If they are alien visitors, why don’t we have better and more definitive forms of evidence? Why is the available video evidence so hard to interpret? Why isn’t there a proverbial “smoking gun” of proof for an alien spacecraft?
This particular counter isn’t entirely convincing. First, the best evidence may be contained in the still-classified materials. Second, the same question can be used against non-alien hypotheses. If the sensor readings were just storms or some other mundane phenomena, surely that would become increasingly obvious over time with better satellite imaging.
The continued, ongoing and indeed intensifying mystery of the sightings seems to militate in favor of a truly unusual explanation. It will favor both the alien-visitation and the religious-miracle hypotheses. If it really were a flock of errant birds, combined with some sensor errors, we would know by now.