Each "character" present in multiple personality disorder has their own views and opinions of the world and themselves. Most people with this disorder were either physically or sexually abused as children. The article talks a little bit about disassociation, a defense mechanism.
Personally I think self-esteem does play into the disorder in some sense. Having an extremely low self-esteem may cause them to create another personality that has a higher self-esteem. Physical and/or sexual abuse can cause low self-esteem. Is it possible that abuse is just the underlying cause? Maybe abuse and self-esteem interact.
Of course, not everybody with a low self-esteem has multiple personalities. Same goes for those who have experienced abuse. The question remains, what else could be a possible factor?

