The Church of Asmodeus teaches implicitly from earliest seminary, and explicitly starting from the 4th circle: that to believe what is advantageous to believe, is urbane, sophisticated, clever, wise, and the way of the winners.
And the proof of this doctrine is the wealth that you gain, at 4th circle, and your tyrannical power. If you doubt your own superiority, you can just go find some naif who spent their lives in naive service to the Good gods, hoping for a pleasant afterlife; and listen to them scream and beg and plead before you Maledict them to just the same Hell you'll go to yourself, but with more unimpressed devils.
By believing what was useful to believe (says the Church of Asmodeus to its 4th-circles, after they have cast a few Maledictions and damned themselves almost as thoroughly as soul-sold wizards) you rose in the world's tyranny, the only real game that real people play; people who claim to be playing some other game instead, are trying to console themselves for being losers at tyranny. You have become wealthier by far than the naive people who go around naively imagining that they try to believe what is true. You can hurt them, and that's the proof that you're the winner.
Anyone who tries to claim otherwise is resentful about how they don't get to be wealthy 4th-circle clerics of Asmodeus; and about how they didn't get to win -- defined as hurting other people even more than you get hurt yourself.