If one accepts and agrees on fighting for an unknown war, they must subject ourselves to rules and discipline. Such is the way of a clan or an army. Things must have an order and they cannot be chaotic; allowing their warriors to do whatever they wish will create chaos.

[and it's actually a good thing for Demona's objectives, but it can be a two edged knife. Humans hate to be told what to do and they could get nasty for having Shibusen forcing them to follow certain rules regarding fights]