Why did some southerners particularly in the Upper South criticize slavery?

Some southerners in the Upper South criticized slavery due to economic considerations, believing that free labor would be more productive and lead to greater prosperity. They were also influenced by moral arguments against the institution, viewing it as incompatible with American democratic ideals. Additionally, the rise of abolitionist sentiment in the North and the fear of slave uprisings led some to question the sustainability and ethics of slavery. These factors contributed to a growing debate about the future of slavery even among those who benefited from it.