As some have pointed out, an excellent argument for serious consideration of non-human involvement with humanity in ancient times is the great number of mysteries that would resolve if it were true.
I believe a sort of converse of this is also correct....
In order for the idea of non-human involvement over the last 50,000 or so years to be true, these types of mysteries would have to exist in our past.
And they do.
I grew up in the US. They way we were schooled... the idea of aliens in our past was incorporated by me as some neo-thought process (Daniken). A product of the collective conscience of humans to find some mystery in the world today. A collective hope that somethings are still left undiscovered. Lenord Nemoy on Friday night with his "In Search Of" programs and the like were thought of as.... entertainment.
In my later years I have learned that in just about every ancient culture. There appears to be a strong suspicion if not down right general knowledge of star people, visitors, watchers... whatever you want to call them in our ancient past. In fact, the pattern mimics the current one. It seems some people knew what was going on... and didn't want to tell everybody outright. Either because they knew they wouldn't be understood\believed.... or they knew they shouldn't.
While 'they' may be the reason for the 'many' gods in some cultures. What strikes me as profound is.... they seem to be responsible for AT LEAST the promotion of monotheism, if not the origin of it. Which has always begged the question.... Are aliens religious, in our sense of the word?