Why does MPD keep making its periodic comebacks, despite not being a verifiable or clinically useful mental disorder? My best guess is that the labeling of 'alters' offers an appealing and dramatic metaphor, an idiom of distress.
Whether a person's "identities" can be dissociated or not, it's clear from Hans' story that certain aspects of a mind can become somehow "out of step" from one another. And that's essentially what neuroscientists think is happening in a schizophrenic person's brain.
The cases of Multiple Personality Disorder are far higher in North America than in any other part of the world. Many suspect that this surplus is the product of U.S. culture and over-indulgent psychiatrists and psychotherapists.