'Suspiria'

What is it about witches that makes them so much more horrifying than other supernatural beings in film?

I think it's because unlike vampires, Frankenstein, ghosts and whatnot, a witch chooses a certain path and that route has everything to do with conjuring Satan. Those others don't have a choice. Frankenstein was made. Vampires are victims of other vampires. Ghosts just want some sort of end to their existence.

Witches, on the other hand, have a yen for evil and the dark side of spirituality. So they get together and start dealing with the devil, quite literally.

Suspiria, I've got to admit threw me for a loop. I didn't know where everything was going until our heroine did and when it happen it scared the bejesus out of me. Much in the same vein of the jokers in Rosemary's Baby, the thought that witches are just ominiously lurking about looking for an unsuspected person to improve their cause triples the oddness of the witch. Witches also do creepy things like brainwash, snip people's hair, brew concoctions and harrass filmmakers like in The Blair Witch Project, which was creepy too.

According to the co-writer on the film, it was inspired by the experiences of her grandmother. We are thus led to believe that her grandmother was taught by a coven of witches at a dance school in Munich. I guess.