>>96052942
Warhammer Fantasy cults function that way too in-universe.

A lot of cults are hidden in purpose. A new cult following finds some new form of "heresy"/"witchcraft" that seems to work, that is somehow healing people of their boils/ailments, but is actually manifesting Nurgle's corruption until it's too late and people start to decay and rot, ala "The Society of Harmonious Growth and Splendour". Another cult has elitist faggots running off into secret orgy hideouts engaging in all manner of fetishism, but are actually manifesting Slaanesh's influence and it gets to a point where the people engage in more depraved acts. Some have that one person who is seeking favor/power from the gods and ropes everyone into his scheme/corruption.

The focus is on the sin to excess.