The Conspiracy Theories of Area 51

Astronauts at the nuclear test site near Area 51 tested various space equipment, including land rovers. It's not hard to imagine a curious employee spotting some of this equipment and helping to stoke the fires of the conspiracy theorists. The wildcard theory is that aliens are in charge and have slowly taken over humanity through Area 51. This one is impossible to prove for obvious reasons, because if it is true, they're already controlling what we think.