It is very difficult to prove that imaginary things are not real.
Imaginary things are, but not limited to: Werewolves, Vampires, Santa, Bigfoot, insert well known omnipotent being here, Unicorns, Loc Ness Monster, etc...
The burden of proof lies on those that claim that something is real. Because cannot produce any real evidence, they will usually construct a conspiracy theory, then say that those that disagree are part of that theory.