For the entire time I was a JW (1999-2007) I never believed in demons.
A few times I remember this getting me into small confrontations with JWs. A JW would talk about how demons were scary and powerful. I would argue that I've never seen a demon, and that to be affraid of such things was silly. They would argue back that I was "careless" and could be putting myself in danger.
Before I was a JW I remember playing ouija board. I remember pushing the planchette towards certain letters and words as a joke. "Are you stupid?" I would ask, as I pushed the planchette towards the word "yes". My friend was terrified that I was potentially irritating spirits, I found it to be one giant farce.
This attitude never left me. Even during my most dedicated moments as a JW I would cringe when talk of oujie boards, spirits and demons were discussed as being dangerous.
In the end, I think South Park summed it up the best: