I hesitate to use the word "disorder", whether the term be MPD or DID. I majored in Abnormal Psychology, and am a graduate social worker, and practical nurse (retired from both). I also do not agree with the fact that we study MP in the form of Abn psych, for who is to say being part of a system is abnormal?
I am quite well aquainted with one individual, who is part of a system. Each member has their own role to play, in helping the system as a whole, just like each member of a singleton family has their role within that home.
In abn psych, we were taught that through counselling, the different personalities would intergrate as issues were resolved, to help the "core" or host body, to become "normal" so to speak. I have since learned that this is not always the case. While some multiples do want to intergrate, I have found that many do not. They work well together, and each person within that system has their own function, likes, dislikes, friends and so on.
There is far too much that we do not know about MP for us to ever to say it is abnormal, or it is a disorder. A disorder is something that is not orderly, and from what I have seen with this particular person, their system is quite orderly, helping each other when times are tough, encouraging and protecting when needed, just as we "singletons" would do with our friends and family members.
I do agree that educating singleton's is the only way to help us to understand, and by having people such as those who are part of a system to post here, we can learn. Let's try and forget what we have learned in abn psych, and learn from those who really know what it is like. After all, experience is a great teacher. :)