Are scary tales good for children?

The original Fairy Tales were often dark, scary tales, but were intended for children.

• Are scary tales good for children?
• If so, what can be gained by reading a scary story to a child?
• If not, why are they bad?
• What are these stories really about?
• What is the purpose of these stories?  What do the teach children?
• Do they succeed in teaching their lessons today?