Corruptible assumes they weren't started for that purpose in the first place.

I wish there was a way to know what the mix of true believers and opportunists involved in each of the religions' founding. Like the story of Constantine includes elements of both (he wanted a way to increase the unity across the Empire because it was getting hard to convince Iberian Romans to take up arms for wars in the middle East, but there's also a story that he dreamed about having a cross on this shield leading to winning a battle). That wasn't the founding of Christianity, but it is the reason Europe adopted it.

Or looking at the old testament, it seems to be a combination of general living advice/laws, events based on actual historic things (like David and Solomon were probably real), and stuff likely made up after the fact (like Genesis). I'd say the ones who made up Genesis weren't likely true believers (of what they were writing), but it's hard to say if they believed in the rest of it and just wanted to fill the gaps in good faith, or enjoyed the clerical power and filled in those blanks because not filling them in would have threatened that power. Or some combination of the two.