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Yes, yes, now that's what I like to hear. The indomitable spirit and righteous indignation of the human species. I've heard it a million times defending a billion atrocities, and it's still music to my ears.
— The Devil • Brimstone

Behind the line May contain spoilers.
Our reading
An editorial interpretation.
The speaker welcomes human indignation while claiming it has repeatedly defended atrocities. Calling it music turns moral outrage into something pleasurable to a hostile listener. The disturbing joke lies in the suggestion that feeling righteous can accompany wrongdoing rather than reliably prevent it.
Context reviewed