Missed the point. Abu Ghraib demonstrated that the principles of the Zimbardo prison experiment apply in real life. American soldiers treated prisoners ways that are not acceptable given the dynamic of the social situation.
Thus, given the right social circumstances members of even our Republic can become instruments of unacceptable action and oppression.
That negates the counter argument that tyranny could not happen here.
Very simple. If you want to argue that it wasn't bad there - you didn't get the rationale.