In the end, isn't it academic, this notion of what is demon possession? On the one hand, you have a raving lunatic, maybe spouting blasphemies, whatever, on the other an unbeliever, let's say a football fan who knows the stats of every player, who could pass psychological tests with flying colors. How are they different? You say the first one is possessed, but not the other? Somebody who's totally absorbed by the demonic entertainment culture, that's designed to have you doing everything but thinking of the the things of God, which could even be obsessive stamp collecting or raising orchids a person's idol, but somebody seeking all things of the world, the flesh and the devil, with disregard for God, is that person not also possessed in another very real way? Is that person, or is that person not, a very slave to sin and the devil? Wouldn't you call this a very real form of possession, blinded by the world to the things of God? Is a slave, or is a slave not, a possession of the master?
People seem to have a very high threshold of what they'll call evil. But, in God's economy, anything that replaces the things of the Lord in peoples' hearts and minds is evil. Consider this, how the Lord Jesus actually called what would be considered good, responsible family men, who do good things for their children, evil. Do you think perhaps God has a different standard than society of what, in fact, is evil?
Matthew 7:11 If ye then, being evil, know how to give good gifts unto your children, how much more shall your Father which is in heaven give good things to them that ask him?
That verse is interesting, in that those who surely love and give good things to their children are called evil. In fact, God's tolerance is zero sin, when it comes to whether or not a person faces hell and damnation. A person can easily go to hell over a life dedicated to football.
If you believe demon possession is just somebody talking to hallucinations and ripping at their hair, think of all those in the culture slaves to the Godless, Satanic world. It really seems academic, whether somebody goes to eternal damnation with a hundred personalities, or with one personality, who knows all the statistics of a hundred ball players.
Did anybody see that science fiction movie, about a guy who found these special sunglasses, that made him able to see the skeleton-like faces of the alien people who were really controlling the world? I believe, if this were possible, you'd be surprised how many demonic skeletors there are out there, feeding you a steady diet of the world, the flesh and devil, teaching you that sitting around a campfire and getting crocked on beer is as good as things get, silk hats on pigs galore, sinking the whole culture deeper into sin, like boiled frogs. Skeletors in your neighborhood, skeletors at the shopping mall. Add to that Christians, driving "under the influence" on, say, message boards. And does a person have to be clinically mentally ill to be literally as sick as hell, in eternal matters, that is, with regard to the only things important?
Luke 18:10-14 Two men went up into the temple to pray; the one a Pharisee, and the other a publican. The Pharisee stood and prayed thus with himself, God, I thank thee, that I am not as other men are, extortioners, unjust, adulterers, or even as this publican. I fast twice in the week, I give tithes of all that I possess. And the publican, standing afar off, would not lift up so much as his eyes unto heaven, but smote upon his breast, saying, God be merciful to me a sinner. I tell you, this man went down to his house justified rather than the other: for every one that exalteth himself shall be abased; and he that humbleth himself shall be exalted.