The more I think about it, the more I think the Dark Brotherhood actually could work if it were written by someone with any idea how cults operate.
Like say they recruit like in Oblivion, they find people who've killed (or anyone with a sufficiently high bounty) and approach them out of the blue - with completely different dialogue & framing this could work so much better. You're probably on the run from the law, alone and vulnerable, that's prime cult recruitment fare, so instead of Lucien being all "muahaha you're evil like me" make him a smooth, comforting presence, he shows up and offers you sanctuary and a family who can protect you, make sure you're safe forever and nobody will ever come after you again. Don't even give the trial contract, just hand over the Blade of Woe and invite them to the Sanctuary, making it clear he expects your presence - if you don't show in a couple of days he'll come back and give you an oh-so-friendly reminder, and if that doesn't work then other members will ensure you never do. Let him show up in the middle of the night still too, just to make it clear that despite the friendly welcoming air he knows who you are, knows you're vulnerable and can reach you anywhere.
Then, all the early contracts should be easy, simple jobs against targets you're told deserve it - corrupt guards, abusers, that sort of thing - and your "family" are all so comforting and reassuring and encouraging, after all this isn't that different to what you did before, and your family are more experienced and always willing to support new members; after all, the rest of the world hates you now, so who else do you have for support?
When you're deeper in, the contracts start getting more difficult to justify to yourself, but what else could you do at that point? You can't just leave, you know very well by now that the family would be able to find you anywhere and even if it's never mentioned you know there's only one way out, and telling the guard would be confessing to enough murders to earn you an execution anyway. It's not until around this point that they even mention Sithis - before now it's just been a family that takes special jobs in a form of unspoken public service, it's only when you're fully entrenched and can't afford to question it (for your own piece of mind as much as anything) that all the truly dark religious aspects get brought in, and things only get more unpleasant and disturbing from there.
