Keep in mind that in the 1970's Hollywood was more blatant & arrogant than it is now.

The Exorcist movie is one of the best primers in how they take children & use them to get access to Adrenochrome.

When the child Regan is possessed the demon makes her suffer and puts the child's body into a lot of pain. Again a technique to gain access to adrenochrome.

Also keep in mind at the end of the movie there is no happy ending. The child is ruined, a family is broken, one of the priests is dead, and the demon is still free to do what it wants.