Can we trust our Moral Intuitions?

[Spongebob]

Maybe give it a second thought.  The op was describing moral views as a product of cultural norms, and how this is an issue for ethical theories like non natural realism.   With respect to lincoln - both those views we would describe as good today and those we might describe as bad today were, as you yourself note, influenced by the circumstances of his birth and upbringing.  All of this, and not just the one set, were his moral intuitions (or..at least would be, in that view).

Our societies produce complex moral characters with conflicting imperatives varying categories of intent.

Your post was directed mostly at historical revisionism, not cultural influence on morals.  If you want to assert the cultural influences on those who opposed slavery, then that's relevant.  The point is simply this, if moral objectivity is a myth and morality is completely relative and highly influenced by culture/society, then what causes the outliers in society who buck cultural moral norms?  Where does that tendency to deviate from what culture says is moral come from?  What causes it?  I used Lincoln as one example but I'm certain there are plenty of others.  And perhaps it's not right to pinpoint one human but ponder the likelihood of a small network of outliers.  But then what causes that network to deviate?  Where does the first point of deviation come from?  And why?