I really wish I was wrong.

From Catholic.com:

The Ouija board is far from harmless, as it is a form of divination (seeking information from supernatural sources). The fact of the matter is, the Ouija board really does work, and the only “spirits” that will be contacted through it are evil ones.

Here is a CBC article talking about how the Ouija board actually works basically the way I described:

Researchers at the University of British Columbia are using Ouija boards to test human intelligence.

Docky Duncan with UBC’s Visual Cognition Lab says the spirit board traditionally used to channel the dead can also be used to test people’s unconscious knowledge. He says it’s not ghosts moving the board, but users’ ideomotor reflex.

“The movements that you see on a Ouija board are unconscious movements. They are produced by the players themselves, but they don’t feel responsibility for them,” said Duncan.

To test this theory, Duncan has blindfolded subjects place their fingers on the planchette — or the triangular piece of wood that moves across the board — and then asks them yes or no questions. So far, he has found that most people answer two out of every three questions correctly, even if they think they don’t know the answer.

"Ask someone if they know, you know, ‘What’s the capital of Cambodia?’ and they might say, ‘I have no idea.’ But they might have heard it somewhere, and it may actually be inside your brain somewhere," said Duncan.

“When we ask people these questions using these unconscious answers, suddenly players can actually access that knowledge and it really becomes manifested.”