Who thinks up such stuff? It's incredibly cliché, almost a caricature. I mean, yes, it's religion, no guardrails against jumping off the deep end, but I can't take it seriously. They could at least try to make things make sense from the perspective of Sharran theology, but what do we get: EEEEEVILLLLL, HARHAR.
I think the purpose was to get clear antagonists you didn't have to second guess killing. If you meet a Sharran cult you don't want to be worrying any of them are just confused or lost people who have suffered and been seduced in without understanding what Shar is all about. Good or bad that was what D&D was built for, at least back in the early days.
I recall this kind of stuff being one of the reasons why I've always disliked D&D. What kind of roleplaying is it if you don't have to make a decision about who to kill, just about how to kill? And why? "Everyone knows they're all evil". I don't want to play in a world where that works.
