this guy is actually trying to justify slavery
Slavery existed for most of the entirety of human civilization. It was seen as normal, in many countries particular religions and beliefs still justify slavery. Only one empire worked to eliminate slavery at great cost. Under the tenets that underpin the morality of Christianity specifically, and under the Magna Carta, the British Empire and its colonies worked to eliminate slavery from society, something that had never been attempted or accomplished before, at great personal cost. Slavery, and the current revulsion towards it, would never have been eliminated if it weren't for British Colonialism and the spread of Christian morality. It is not at all surprising for people who don't value Christianity and British Empire to not have the same revulsion towards slavery, or even forced/indentured servitude. Merry Christmas!