The idea that invading spirits are inherently evil is largely a Judeo-Christian concept; many religions and belief systems accept possession by both beneficent and malevolent entities for short periods of time as uncommon — and not especially alarming — aspects of spiritual life. Spiritualism, a religion that flourished across America in the 1800s and is still practiced in a few places today, teaches that death is an illusion and that spirits can possess humans. New Agers have also long embraced a form of possession called channeling, in which spirits of the dead are said to inhabit a medium's body and communicate through them. Hundreds of books, and even some symphonies, have been allegedly composed by spirits.
While many Americans think of real exorcisms as relics of the Dark Ages, exorcisms continue to be performed, often on people who are emotionally and mentally disturbed. Whether those undergoing the exorcism are truly possessed by spirits or demons is another matter entirely. Exorcisms are done on people of strong religious faith. To the extent that exorcisms "work," it is due to the power of suggestion and psychology: If you believe you're possessed (and that an exorcism will cure you), then it just might.