The dumbest, wildest conspiracy theory that I actually kinda believe is that major powers have been planning a fake alien invasion for a long time.

It probably started after Orson Welles "War of the Worlds" radio play. Many folks bought into it. The elites probably thought, "Damn, we could really pull this off for real."

All the UFO-mania of the past several decades is probably a small part that were orchestrated, a large part of people genuinely imagining they saw a UFO or were abducted or whatever, and plenty of the media was encouraged by spooks.