The members of this sect were revolted and even thought about fighting the invaders, but the elders of the Divine Realm told everyone not to resist because the enemy had 21 elders of the Divine Realm and they could not react.
Before coming to this sect Zhang Yi warned that members of that sect would fight when Zhang Yi said that they were investigating the members of the organization, so they were only allowed to hurt the opponent and defend themselves and not attack the sect.
After all, their objective was only the members of the organization and not the entire sect, as this alliance was much stronger this was certainly possible, everyone accepted this because they really did not want to become enemies of that sect.