The word "enlightenment" has a galaxy of different meanings; the experience of depersonalization is one of them, but it's far from the only one, and it's not the goal of every spiritual path -- in the path I follow, for example, the personality is seen as a useful tool, to be cleansed of grime and inappropriate attachments so it can be used constructively. One problem of losing the sense of identity is that it makes self-knowledge very difficult -- and that, in turn, opens the door to a lot of pathologies.