Honestly, I think that many churches tend to stay away from overtly "spiritual" things both good and bad. Most of us would rather learn how to deal with our personal problems, like "how to be a good spouse", or "how to raise kids"...those types of issues appeal to us more than deep issues of the spirit. These human problems, at the heart of them are "spiritual", but we usually will take more of a "psychological" approach to the problem. This is one reason I think that many problems stay unresolved because we fail to include the spiritual side of things.
Some of the churches that do deal with these types of issues are often so "over focused" on the spiritual world- especially the demonic- that it becomes a spectacle or a carnival show. It makes for an exciting "show". The glory is given to the "minister" who smacks the guy on the head, instead of giving glory to God who heals and delivers. In the end--the world discredits Christians as being a bunch of wack-a-doddles.
Demon possession is impossible for a follower of Christ as it is God's spirit that resides in us. We can, however, be harassed by demonic spirits. In that regard, we stand on our authority as a child of God and the demons have no right to harass us. We need to recognize when this happens, however, and stand in our authority. Sometimes we miss this as the heart if the problem.
If someone is a non-believer and you cast out the demons-- they will often come back if that person doesn't become a Christian.
"When an evil spirit comes out of a man, it goes through arid places seeking rest and does not find it. Then it says, 'I will return to the house I left.' When it arrives, it finds the house swept clean and put in order. Then it goes and takes seven other spirits more wicked than itself, and they go in and live there. And the final condition of that man is worse than the first."
The best way to drive out a demon is permanently by the indwelling Holy Spirit.