Black Magic is Not a Myth in Articles by Aleister Crowley.

“Spiritists are playing with malicious forces.” [via, also]

Consider also:

  1. “Through their mediumistic acts, spiritists sometimes get hold of disintegrated pieces of the mental apparatus of a man or woman who has died recently.”
  2. “In the congregational form of the Black Mass the priest, having finished his abominations–these are, quite frankly, indescribable–scatters the fragments of the Host on the floor, and the assistants scramble for the soiled fragments, the possession of which, they believe, will allow them to work their petty and malicious designs.”
  3. “Of course there are forces which are definitely malicious. It is never necessary for a magician to deal with them, except as a bacteriologist studies disease germs, to find out their nature and subdue them.”
  4. “Then the fun began. We saw–and my teacher was able to identify–hundreds of shapes, weird “half-formed faces” which were thronging the room, marching in fantastic dance about its confines. These were definitely malicious forces, demons, which one had to study and conquer.”
  5. “My most memorable personal experience of the effects of black magic occurred when I was living in Scotland. The machinations of a degraded and outcast member of the Order caused my hounds to die, my servants to become insane. The struggle lasted until the recoil of the current of hated caused the luckless sorcerer to collapse.”