Aliens have not been "revisiting us for centuries now". Because there is not a single shred of physical evidence supporting such an assertion.
Or are you going to claim that the aliens, or the US government, or the UN, or the Chinese, or the Freemasons, or the Trilateral Commission, or the Jewish bankers have been able to locate and hide every scrap of evidence, kidnap and silence every witness, divert every researcher, buy off every scientist and blackmail every official in the entire world for lo these many years?
You cannot objectively say there is no evidence
Looking at it objectively, I say, "There is no evidence."
Evidence is substantiated facts that logically support of a claim.
Let me tell you about Arnold Trimble, who, in 1732, claimed that cats heard through their legs. To prove this, he placed a cat on a table, and fired a pistol behind it - the cat ran away.
Trimble then cut off the cat's legs and did the same thing. The cat did not move, thus proving that cats hear through their legs.
Now, was there objective evidence that cats hear through their legs?
There are facts out there, but no evidence to ascribe them to aliens or even as proof of aliens.
For every event credited to aliens, it would be possible to substitute the word "fairy" for alien, and thus prove fairies.
Do you believe in fairies?
All of this Erich von Daniken rubbish is tiresome sloppy thinking designed to sell books to the gullible. Look on it as a tax on stupidity.
What you can say is, you've been made aware of evidence and that some very knowledgeable people who have looked at it have not found anything conclusive
i.e. there is no evidence.