This is a linkpost for https://atheistkit.wordpress.com/ethics/
Someone could be against slavery for THEM personally without being against slavery in general if they didn't realize that what was wrong for them was also wrong for others.
Huh? I'm against going to jail personally without being against the idea of jail in general. In any case, wasn't your original argument that ancient Greeks and Romans just didn't understand what does it mean to be a slave? That clearly does not hold.
most moral theories are so bad you don't even need to talk about evidence. You can show them to be wrong just because they're incoherent or self-contradictory.
Do you mean descriptive or prescriptive moral theories? If descriptive, humans are incoherent and self-contradictory.
Which moral theories do you have in mind? A few examples will help.
Mmm, that's not quite the right abstraction. You're probably against innocents going to jail in general, no?
Whereas some Roman might not care, as long as it's no one they care about.
All I'm getting at is that the Romans didn't think certain things were wrong, but if they were shown in a sufficiently deep way everything we know, they would be moved by it, whereas if we were shown everything they know, we would not find it persuasive of their position. Neither would they, after they had seen what we've seen.
I'm talking metaethics, what makes something moral,...