Damnit, people insisting on this. Kaneki does not have a million people living in his head. He is a character who goes through significant development at several points in the story. Just because the, I don't know, the Goku or the Naruto at the end of the series is not the same as the one they were at the middle or at the beginning of the series doesn't mean that their past versions still exist inside his head. Haise is Kaneki without his memories. The little Kaneki was just a representation of the memories he repressed.