it's like the alarm call of various animals; say an individual monkey spots a predator, and gives an alarm call, then it might have benefited that species ancestors to spread that alarm call, even though only one monkey may actually have seen something. Any species that doesn't have a time limit of this sort of behaviour will spend it's time giving perpetual alarms and will die out.
With a conspiracy theory, only one monkey need give the alarm, and he/she may have been mistaken, but it seems like a fairly good system, to me.