He was just using that as an example where we should question our assumptions. Particularly when the subject comes with many 'common sense' automatic assumptions it's good to give extra scrutiny to the subject.

You don't have to be doing something "by default" in order to prove or disprove an hypothesis.

There is more the enough historical evidence that any type of violence or extreme pressure creates false confessions. Nor do you have to rip off someone's fingernails to find out humans will tell you anything to make it stop. You can always extrapolate from more humane experiments, if data from a previous era is not available.