Do you believe in demons? (Luke 6:17-19)

Luke 6:17-19 ¹⁷ Jesus came down with them and stood on a level place, with a great crowd of his disciples and a great multitude of people from all Judea, Jerusalem, and the coast of Tyre and Sidon. ¹⁸ They had come to hear him and to be healed of their diseases; and those who were troubled with unclean spirits were cured. ¹⁹ And all in the crowd were trying to touch him, for power came out from him and healed all of them.
Luke was a medical doctor and the author of this gospel.   And in these verses he differentiates between those with physical diseases and those with unclean spirits.  He certainly believed in what was commonly called demons or unclean spirits.  The companion passages in the other gospels tell a similar story:

Matthew 4:24-25 ²⁴ So Jesus' fame spread throughout all Syria, and they brought to him all the sick, those who were afflicted with various diseases and pains, demoniacs, epileptics, and paralytics, and he cured them. ²⁵ And great crowds followed him from Galilee, the Decapolis, Jerusalem, Judea, and from beyond the Jordan.

Mark 3:7-12 ⁷ Jesus departed with his disciples to the sea, and a great multitude from Galilee followed him; ⁸ hearing all that he was doing, they came to him in great numbers from Judea, Jerusalem, Idumea, beyond the Jordan, and the region around Tyre and Sidon. ⁹ He told his disciples to have a boat ready for him because of the crowd, so that they would not crush him; ¹⁰ for he had cured many, so that all who had diseases pressed upon him to touch him. ¹¹ Whenever the unclean spirits saw him, they fell down before him and shouted, "You are the Son of God!" ¹² But he sternly ordered them not to make him known.

You know, in seminary they didn't teach us about demons.  Or about how to cast them out.  In fact, they didn't teach us how to heal either.  When I was interning at children's hospital, I asked our chaplain-instructor why they were only teaching us how to comfort people rather than heal them?  I don't think anyone had asked him that recently.  He laughed for a second.  Then said, "Hmm... how would you teach a class in healing?"  I have no idea.  Yet, it was a huge part of Jesus' ministry.  And he said it would be part of our lives as his followers too.

Many have reasoned that unclean spirits were nothing more than mental illnesses.  Yet, these demons talked to Jesus everywhere he encountered him.  They knew who he was - called him by name.  This isn't symptomatic of a mental illness - maybe mass hysteria - but the people he healed had often had the unclean spirit for years before Jesus was well known. 

Do you believe in demons?  I guess the good news is that whatever they are and were, Jesus has power over them.  He gave his followers power over them too.