Sorry, but malicious spirits, aka demons, have historically been around long before any of the JCI religions so you can hardly put the blame on them. Demons exist in almost every human mythology, and were believed to be responsible for the ills of mankind. The Native tribes spoke of demons in their stories. The Sumerians, Babylonians, and Akkadians, believed in demons (and are, in fact, the inspiration for what eventually became the Judaic mythology). The Japanese had all sorts of demons lurking in their forests, lakes and valleys. The ancient Greeks had demons, and devils, and monsters. You can find demons in stories from practically every corner of the world, and yes, in almost every story, they are said to be mostly harmful.