Actually it's a very useful role for a philosopher, one cherished from the time of Socrates down to Nietchze, Adorno, Christopher Lasch, and almost everybody else in between.
>Well which is it? Are we truly to believe that the horrific demonstrations of torture which Foucault spends entire chapters chronicling (salaciously, like pornography) did not frighten anyone?
Yes. And in fact you can find tons of sources stating that they were kind of public spectacles, with women, children and others participating -- even until down to the early 20th century.
>Why if so does he describe them in such detailed fashion?
This question does not follow from anything. You essentially ask "if they didn't frighten anything, why does he describe them in such detailed fashion" -- as if how detailed their descriptions are, is supposed to be affected by whether they frightened people. I, for one, fail to see any mystery or contradiction. You can describe in minute detail also stuff that doesn't frighten people.