But I would argue that regardless of the time or society, people are the same. The rules they will play by change but they will still seek to satisfy their instinctual desires. Just as we have people today who conduct activities that society considers wrong, so did the medieval societies. The 'evil' we see today is not new to our society, it may be desires manifesting themselves in different ways, but the conduct of people does not change.
You argue that people ARE the same. I argue that people COULD be different. Burden of proof on you.