There is an important part of being in a death cult that I think we don’t think about often enough as game masters. First - What do we mean by “death cult”? Most FRPGs have gods of death and these gods have worshippers. While some of these religions are serious and upstanding members of society, some of them are “death cults”. These cults worship the concept of death. They enjoy sending folks to their gods of death and feel that mass murder is “holy”. Further, many of their members are actually seeking death. Maybe they feel that suicide is “good” but lack the will to do it, so they join the death cult hoping to get closer to death by killing others and possibly getting killed themselves. This is sort of a “suicide by cop” or suicide by adventurer. This explanation is not very good, because we’re trying to cover far too broad a topic. Not every suicide cult or death religion is the same, or even all that similar, so broad generalities don’t work.
So what is the important point that I think you’re forgetting? The members of death/suicide cults are losers! People with confidence and who will be a benefit to society don’t join death cults. Guys who are infatuated with their thoughts of six dozen wives in the afterlife are probably the kind of folks who can’t get one in the mortal world. Why is this important? It matters because the NPCs in these cults should not be assumed to act like “normal” people. They aren’t going to be soldiers who stand at post or agents carrying out secret missions with the skills of James Bond. They are going to be the loser bullies you knew in high school, the followers of those bullies, or the folks who weren’t just goth, but the ones who needed to constantly tell you they were goth and that’s what made them better than you. You know - the losers!
Yeah - I know - most of us FRPG players were considered geeks and even losers in high school, but the vast majority of us are working to make legitimate lives for ourselves. We’re not out looking for the fast track to heaven by wrecking harm on others. The death cult members are (looking for that fast track). So what should you do? You should assume that the members of these death cults are: unintelligent, bullies, followers, dedicated to their cause, cowardly, and typically chaotic. These are the types of people we’re talking about; people who either due to a lack of confidence or reason believe that there is nothing they can do to succeed in the normal fashion and therefore turn to concepts and organizations that are blatantly idiotic to the rest of us. Our world is filled with these folks (unfortunately). Too many examples present themselves. school shooters, terrorists, etc. Sometimes chaos needs to not only be role-played, but actually affects the outcome of the mission.