demons when posses human be can make the person have an experience beyoung his ability. A demon when posses you can give you accesse to hiding knowledge, speaking of foreign languages, and drastic changes in vocal intonation, focial structure and change in eye colour. In the other hand demons can couse diseases and can make someone behave abnormal. Demons are not good intite becouse there full of weakness and hate for human kind. Demons are energy dranners.
This description is full of stuff derived from the witch trials as much as it is derived from fact. Possessions can alter an individual's speech, it can give the impression of altered facial structure due to altered facial mannerisms, and sometimes the individual speaks of things that they might not otherwise have not known. Demons are not the only spirits that might possess an individual this way, and in some traditions spirits of both good and bad nature are actively channeled into one's body.
Further, Demons are rather vast entities, that have little care for your existence in most cases, let alone wanting to bother with something so extreme as hatred. Many lesser spirits, that might be called demons, are hateful and vengeful and so forth because it is how they attempt to imitate higher emotion.
I agree that demons have little to no care for your existence. They exist on a different level than we do, and have different things to worry about than just messing with humans via possession. They can help you, it they can really mess you up. Ultimately though, they tend to leave you alone unless you summon them or disrespect them in some way. Demons are sometimes summoned to help in a spell or with some kind of work. When they are summoned you should be immensely respectful, and understand that they do not have to do anything you say. Some people get cocky, think they can do anything, and demand the demons to do this or that. I view demons in a way like humans. They have free will, are notall different, and may respond in different ways.
I do not believe that they hold a hatred toward humans. They are not like us emotionally. They exist on a different level than us, as I've said. They wouldn't even stay in one place for a long length of time of they're own free will.