Däniken makes the case that what humanity thought of as gods in the past are actually aliens. We are the result of their breeding programs. Ancient monuments too sophisticated for the peoples of their times were built using the technology of the aliens to demonstrate our readiness of their return.
The evidence is viewed with the strongest optimism. In my more skeptical eyes it comes up wanting. Things presented as supposition are later used as fact to make more supposition still later used as fact. In this way the case becomes more and more fragile instead of stronger.
That people take this seriously is disturbing.