Look, Keltham was raised in a way where, if one single member of the Hypothetical Conspiracy had managed to broadcast to the rest of Civilization the whole truth about the Conspiracy's grimdark misdeeds, and told them where to look for evidence and proof, and then demanded a billion gold pieces in exchange for that, plus that the next few attractive true-murderers of the appropriate sex be turned over to them for sadistic purposes, as would be less than one ten-thousandth the number of victims under the previous regime, etcetera, the obvious thing to do would have been to pay them after you'd overthrown the Conspiracy.
There is very plausibly a non-Dark Conspiracy using 2% of Civilization's resources on something important and terribly secret. You can tell this because Keltham has - in fact, now that he reflects on it - been brought up in a way that would make him feel like this is the obviously right and proper thing to do, if you have some important thing to be running a non-Dark Conspiracy about; and everybody would owe the Keepers and upper Governance gratitude for having taken on this secret duty.
If there was a Dark Conspiracy, Keltham should have been raised much more on a diet of messages about how, in Hypothetical Dark Conspiracy Dath Ilans, if you try to blow the whistle on them instead of joining them for scraps at the table, they will inevitably catch you and turn you over to their sadists to be made use of, and then tossed to the true death when they're done with you.
And not raised, as Keltham actually was raised, on a steady diet of fictional messages about how, in a world like that, you need to keep the secret and organize with your friends and overthrow the Conspiracy.
Or the decision theory about how to coordinate counter-conspiracies like that, how to wait for an obvious beacon-time to naturally occur, like a solar eclipse or something, and have 10% of the population shout "NOW!" followed by the other 90% shouting "NOW!" and suddenly turning on their hypothetical Dark Overlords.
The Dark Conspiracy that supposedly rules dath ilan is really impressively faking the part where the ordinary people like Keltham are being brought up in a way that makes the Dark Conspiracy's life more difficult and dangerous. If they're trying to countersignal to Keltham how Ordinary they are using costly signals, that plot really-ass succeeded. Keltham wouldn't do that if he were the Conspiracy.