I was watching the History Channel series Ancient Aliens on Netflix the other day and while it's entertaining, it's also somewhat maddening. It's worse than ignorant speculation; it's pure pseudoscience, and vigorously so.
Rather than forming a hypothesis and testing it out --that is, having a question you seek to answer-- the ancient astronaut theorists already have the answer: the aliens did it. It's an answer in search of a question.
Who built the pyramids? The aliens did. Who moved those megaliths to Carnac? The aliens did. Why did the Nazca build their lines? For the aliens. The god Apollo? Pagan myth...or alien?
Sorry, guys, but I think human history is a bit more complex than that...