Not an unmixed truth.
Manumission was extremely common for Roman slaves. It included Roman citizenship, a huge perk. The children of freedmen were accepted fully as Romans and could even become senators or political leaders. That contrasts poorly with the permanent color line in the American south.
OTOH, Roman slaves could be, and often were, crucified or tortured to death at their master's whim. On the other other hand, there was very little to prevent an American slave owner from doing the same.
To be fair, slaves were better treated in South Carolina than in Brazil or Jamaica largely because they were more valuable. The closer you were to the source, the less slaves cost and the more you could afford to kill them off with mistreatment and buy new ones.
Saying Soth Carolina slavery was preferable to Jamaican slavery is like saying life under the Soviet style of communism was more humane than North Korea.
Techincally true but slavery,like communism,is a system based on tyranny.