The Cultivation Ethics Charter was considered a common moral law that all the organizations around the Southern Continent adhered to, kind of like how the mortals had their moral laws that were the same across countless regions despite having different cultures for example filial piety to one's parents.
The cultivation world had something similar. The Cultivation Ethics Charter was created out of it. It was a charter that highlighted the ethical responsibilities of cultivators by emphasizing qualities such as candor, honor, and integrity to name a few.
Of course, the irony of the charter wasn't lost on the world considering the brutality of the cultivation world.
However, regardless of how things were, the charter was still needed as it was a form of an anchor for their humanity, otherwise, without it, they would be no different from the fiendish cultivator.