So rules that change with the times, are not "objective"? Are you sure that you understand what that word means?
Because it sounds as if you think that the objective is dogmatic and rigid, and thus to be avoided.
He said that because of the way I defined objective morality. Hados argument is that if the NT was written with objective morality in mind, then it is inconsistent with my view of objective morality. But I didn't come right out and say objective morality implies our morality doesn't change, but I was more criticizing their own view that if their morality changes over time then it is not objective. I illustrated this by saying if their morality changes over time, then it is not objective. I said this illustrated by saying, "Is it always wrong to torture a baby for fun? If it is, then objective morality exists."
I don't say this to criticize you, but to inform you.
From an emotional POV, you're
both right. It's wrong to torture a baby for fun. It's wrong to enslave a person.
From an intellectual POV, you're both wrong.
Has torturing and killing babies ever been considered moral? What about babies of slaves and captives in wars? In the Roman Empire, it was legal to beat, rape and kill a slave that you owned. A Pharaoh of the Egyptian Empire made it legal to drown some of the male slave babies. The Greeks tell a story of how a baby was put in a big jar and left in a forest to be eaten by wolves (Oedipus).
Has slavery ever been considered moral? Look at the Roman Empire, the Greek Empire and the Egyptian Empire.
These things are subjective to the culture of the society they refer to.
It's grossly unfair to consider them otherwise, and it makes the discussion lacking understanding and so unlikely to be fruitful.
I would be open to hearing an erudite argument why everyone who grew up in the Roman Empire would naturally conclude that slavery is immoral and should be banned.