As a science-y person, I'm not expected to put any weight into religious ideas. But a fucking voodoo doll is a scary-ass concept. And all the sacrificing and bloodletting and dancing and frightening costumes and - lest we forget - actual zombies? Fuck that noise. I don't want it anywhere near me.
Man, think of all the things you could do to a voodoo doll. Pin in the lower back is one thing, but you could dip that bugger into a pile of bullet ants, or blow second hand smoke in its face to give someone cancer, or play a game of battery acid to the front butt. If you're nasty and creative, there's no bloody limit.
Plus, there's the horror of never knowing. Go to all the doctors you want. They won't have a clue. And you'll never suspect the truth.
Short Answer: Further reading: The Serpent and the Rainbow. Also, if I offended any evil priests with my stereotypes, I'm super fucking sorry.