Again, I agree that some things can be subjective. However, when Zaros' army primarily consists of creatures that i.e. must eat people to survive (vampires), then it becomes difficult to argue that it's simply a conflict of geography. One potentially plausible way to reconcile these differing viewpoints would be if Zaros were the Runescape god of monsters. Then it would make sense that he would support those creatures who eat humans, while others like Saradomin oppose them. Zaros has an opportunity to get the support of demons, vampires etc. who are all one of the strongest beings there is. I could perfectly understand why he would recruit them in his army.