There are certain ideas that I find completely acceptable in the context of science-fiction, but completely looney in the context of actual science.
Take, for instance, Erich von Däniken’s premise that gods were really ancient alien astronauts. It’s an interesting idea, but it’s way out there in terms of science. It assumes that (a) myths are historically accurate, (b) aliens exist, and (c) low-tech humans couldn’t possibly have created things like Stonehenge, pyramids, giant stone heads, etc. Not to say it’s not possible that aliens visited the planet in the distant past—just that comparative mythology and architecture aren’t exactly compelling evidence.
On the other hand, I have no problem with the concept in science-fiction. It’s the basic premise of Stargate. The movie and early seasons of SG-1 focused on Egyptian mythology and technology, and in subsequent seasons of the show, just about every ancient legend has turned out to have an alien race behind it. It also figures into the backstory of Babylon 5, with the Vorlons having visited nearly every known race in ancient times, insinuating themselves into local religions and engineering telepaths over the course of centuries.
(via Sclerotic Rings and *** Dave)