Very much, I do believe that people can suffer from multiple personality disorder, it exists, it is there and it can be harmful, because some of them get real crazy.
I believe people can have multiple personalities. I do not know anyone personally who has the affliction. A traumatizing situation I believe is what triggers it from my understanding. Our brain tries to find ways to cope and therefore a multiple personality develops. Although I do not know anyone who suffers from it;I have seem what it does to some celebrities. It seems after they take medicine for it they act normal.
I think trauma, especially in early childhood can cause someone to develop a disassociated personality as a way of coping with something like abuse, but I do not think someone can have dozens of them. That really makes me question if the person is possessed because the human mind does have some limitations on what it can keep track of.
I think in a way we all have more than one personality. It's just that we don't tend to live at the extremes of these personalities - i.e. we tend not to be sociopathic with it. When it does go beyond 'normal' behavior then you've got the bi-polar / schizophrenia space, and that's not a very healthy place to be.
I am not sure I have seen anyone suffer from multiple personalities as it is a very serious disease which cannot be detected very easily. I think it exists for real.*