I like watching Ancient Aliens on History sometimes. I don't believe in it, but I still think the concept is interesting. It's a real spark to the imagination of the wannabe science fiction writer. However, the thing that really annoys me about it is the idea that our ancesntors "couldn't have POSSIBLY built all these awesome things on their own! Aliens had to help!" - That pretty much sells the human race short, basically calling ancient civilizations stupid.
I mean, we don't understand how some of the ancient structures were built. I see that as merely lost technology, not "oh, noes, aliens had to do it." I don't understand the inner workings of my computer just because I use one... so who are we to talk about the lost building techniques of ancient cultures with the assumption that "our ancestors were too dumb to have wonderful lost arts because wah! WE haven't figured them out!" I think it's bad enough when people whine "Bronze Age!" to people who like talking about certain philosophies as if everyone in the past have nothing valuable to leave us even though our world is *built* upon the things they've left us. People always sell the Medievals short, too, forgetting that a lot of scholarship and preserving of knowledge went on during that period. It's really bad enough that we have this kind of temporal jingoism already, we really don't need to pawn off all the things we *like* about the past on aliens just because we seem to think only nowadays living humans are great.