the-incentivized-alignment
That's good progress for a first meeting!
It's terrible news about the dead potential twin Buddha. But it also makes Tanya finally realize something which might be good news in a way, because - "I haven't properly met any drow besides you, Belmarniss. And I've kept thinking about how exceptional you are, and maybe your mother if she raised you this way, and wondering how rare that is, but I somehow failed to make the obvious next inference until now. You're a woman, a mage, from a" - high socioeconomic status - "I assume at least fairly wealthy family. Someone born without your advantages couldn't realistically plan to go to the surface and live here comfortably and safely, and maybe they'd be Good but we wouldn't know it by waiting for more drow to come to Taldor."
"You told me drow worship demon lords because they think they're going to the Abyss anyway and the worship can put them in a better position there, but most people in Noctimar might not think that. Most people in Noctimar are slaves, even half the drow are slaves, and they won't expect things to be any different in the Abyss. Unless the demon lords' clerics tell them otherwise, I guess. They're the ones who'd leap at a chance to be Good, if they can be convinced it's real, because they have nothing to lose and no comforting illusions to discard. I might have thought about this before and concluded it wouldn't work, because the powerful would punish them for - disrespecting or disbelieving in their religion - but maybe they simply won't care? They'll have an incentive to let their slaves and farm-workers go to the sermons, that's where the channels are and they want them to be healthy. And the slaves, the drow males and orcs and halflings, won't find it any easier or more necessary to rebel, they'd just need to wait for their afterlives to be free."
A society of Good people ruled by a mostly Evil elite sounds unstable, but that's only true on Earth. The goal isn't to have a social revolution! If you can get 90% of the population out of the Abyss you're practically done, never mind that they're enslaved in life!
Even something as apparently despicable as 'embrace slave morality and stay slaves' can be justified if the promise of Heaven and the threat of Hell are real. It's a conclusion that feels very uncomfortable but it's rational! (Which is why Tanya should rely on local people more and stop trying to reinvent morality! How did she get stuck trying to reinvent morality? Curse Pharasma for incentivizing that, probably)