There are "parts" of me that do almost exactly that in response to perceived threats -- of rejection, abandonment, or whatever. It doesn't feel to me like having insiders, though, but like shifting in and out of a different state, or mood, or frame of mind.

I can remember when I'd find myself in one state/mood/frame of mind and write out something that I realized in that state, to try to help myself understand it when I was in a different state. When I'd be in the other state, though, what I'd written would seem like just meaningless words. Actually, it worked pretty much the same way in the other direction, too; I might write out in great detail how I felt hopelessly caught in some bind that I seemed to be in, then reread it in a different (clearer, I'd like to think) state and wonder what could possibly have made that bind... binding on me.