There has always been a saying in the Eastern Province, "When All-encompassing meets Senluo, only one will remain."
As long as people from these two Great Teachings meet, they are bound to fight!
However, it seems that due to a rule set by the Founding Ancestors, as long as the other party concedes, acknowledges, and states that the cultivation methods of the other Great Teaching are the most correct, then they will immediately let the other party go.
Of course, people from the Senluo Demonic Sect and the All-encompassing Sect would never concede or say such things. If they did and this got back to their Great Teaching...
Anyone who did such a thing, no matter who they are, even the most talented disciple of the Great Teaching or the descendant of the Sect Hierarch, would be immediately expelled from the Great Teaching.