Hi Lausten,
To say something like “I hold slavery to be immoral, but it is morally Ok (or morally blameless?) for someone to hold slavery as moral if their culture holds it to be moral” sounds like moral relativism to me. But definitions can be tricky.
Flourishing or some form of increased well-being is a goal for moral behavior that I expect virtually everyone could agree on. However…
Talking about the goals of moral behavior leads to what I see as a powerful insight from seeing the science of morality and moral philosophy as non-overlapping domains. The science of morality can tell us what morality is and how it works as cooperation strategies. But this science is essentially silent on what the goals of moral behavior ‘ought’ to be (because that is in moral philosophy’s domain).
Groups could rationally decide to advocate and enforce moral norms consistent with the science of morality (moral norms being parts of cooperation strategies). This leaves the goals of that behavior up to the discretion of whoever is cooperating in a group.
A group could, for example, understand from the science 1) why we would want to follow the Golden Rule, 2) when it would be immoral to follow the Golden Rule, and 3) what to use for moral guidance when the Golden Rule fails us.
Groups could rationally decide to implement a morality based entirely in science so long as they could avoid making unsupportable claims about what the group’s goals and values ought to be.
Imagine these groups cannot agree about what moral philosophy is telling them their moral goals ought to be – the common situation.
No problem! The group would just find shared goals and cooperatively pursue those. I expect those goals would include some kind of flourishing or well-being.
The above is close to defining an attractive moral system based only on science and whatever a group’s shared goals are.