"Multiple personality disorder" is attention-seeking, responsability-dodging lies, and has only became "popular" after Therapists started suggesting it to patients, and exploded after it made its way into pop-culture.

Consider anyone claiming to have multiple personalities to be a liar. Tumblr is full of them, for much LolCow milking. Huge overlap with people who claim to be friends with ghosts of famous dead people, or to be the reincarnation, with extensive / full memories of important people ( yet they can't speak the language or dialect of those people if there is any degree of cultural distance. How strange. ).

Therapists now "work to integrate the different personalities into the whole" aka, "stop lying, it was you who did these stupid things".