I get where you are coming from on the Dwarven story inside MToF. I just don't agree. Could the Dwarven leaders have stepped away, and the rest of the society followed due to their lawful leanings? I mean, maybe it was a question of lawful vs good?The conclusion itself isn't the problem. It is the framing around the conclusion.
Yes, good people can act terribly. That happens. Yes, bad things can happen to good, innocent people. That happens.
But, how we frame those events adds another layer, and the framing in Mordenkainen's Tome of Foes is not just that the Dwarves blamed the Duergar for their plight, but that the Dwarves were not wrong to do so.
We both agree that this course of action was ugly and wrong, but the book presents the story as though the dwarves did the right thing. That what they did was not ugly and wrong, after all, the Duergar are the bad guys and the Dwarves are the good guys. The Duergar are greedy now, they do hate Moradin now, so they must have been greedy and hateful back then, and that is why they were enslaved and tortured.
We are not meant to see the Dwarves choice to cast them out as morally wrong, but morally right.
And that is the problem. You have an event that was ugly, cruel and needless, and it is being framed as the correct course of action for the good dwarves to have taken.
And remember, this is not presented to us as "the dwarven side of the story" this is presented to us from an impartial third party point of view.
Overall, maybe I just don't have the same smarts or experience or depth of knowledge that you do. I concede that you are probably right, even though I see other variables, including the "impartial point of view." But, you are probably right. If it ever comes up at my table, I will try to listen and maybe then I'll see it. But for now, thank you for explaining it to me. It is appreciated.