I'm just so tired of Castle being portrayed as a gullible child buying into any and all supernatural claptrap. I'd think that a mystery writer would be more of a critical thinker and a skeptic. I mean, mystery fiction is all about logical deduction and penetrating deception. It's a cardinal rule of the genre that the writer must play fair with the audience and have a concrete, non-arbitrary explanation for every mysterious thing. Injecting a genuine supernatural element into a mystery would be cheating. (Which is why it's a waste of time when this show tosses a "supernatural" case at Castle and Beckett, because we know going in that it will have a mundane solution, so the oogy-boogy stuff is merely a distraction.)
Granted, Sir Arthur Conan Doyle became interested in spiritualism late in life, but that was due to grief at the loss of several loved ones, and he became rather pathetically gullible, to the point that he believed Houdini had supernatural powers despite Houdini's personal insistence that it was all trickery.
They just want Castle to be a fun character, I don't see the problem. The show itself has always made it clear its light fluff drama.