Indecipherable Scrawlings

I was talking over role play (the kinky kind) experiences with a friend recently.  Between us we had done most of the usual things; doctor, gladiator, interrogator, etc and enjoyed them.  Eventually the conversation meandered to things we wouldn't feel comfortable doing and I brought up an idea myself and an ex had been working on.  One in which I'd play the dark wizard with a maiden strapped to an altar ready to be sacrificed to bring about a dark god.  A nice large pentagram, some candles, and a suitably dark basement would complete the scene nicely.  A scene I had completely rejected.

My friend was confused by this, it sounded like a lot of fun to him.  Until that is I explained my reasoning:

Because that is how horror movies start.