I'm replying to an old post, and will most probably suffer abuse it for it, but here goes anyway.
I have done 1 PhD dissertation - and did not see it as unethical, for the following very simple reason: The student did all the quantitative research, but could not express herself. (This was not Eng Lit, where the ability to use language is integral to the field of study.) I sat with the student, who explained the theoretical framework and the detail of the research, and I simply had to put it all in a coherent whole. Her inability to express herself had nothing to do with the technical aspects of her superb and groundbreaking research in psychometric testing.
So, don't jump in with your negativity.
Ok, ok, I'm waiting to be called anything from retard to ..... (Surprise me!)