Final answer:
The Methodists denounced slavery as sinful due to their belief in equality and Christian principles.
Step-by-step explanation:
The group that denounced slavery as sinful was the Methodists. Methodism emerged in the 18th century as a denomination within Christianity, and its followers strongly opposed the idea of owning slaves. Methodists believed that all individuals were equal in the eyes of God and that slavery was a violation of human dignity and Christian principles.
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