Why can’t science tell us what morality ‘is’?
In the trivial sense, science can certainly catalog the diversity, commonalities, and contradictions of cultural moral standards and moral behaviors.
But science is very good at teasing out underlying principles. What forbids determining such principles (if any exist) using the normal methods of science?
For instance, we might propose an observation like “Almost all moral behaviors are strategies for increasing, on average, the synergistic benefits of cooperation and are unselfish at least in the short term” as an hypothesis about what moral behaviors ‘are’.
Then we could evaluate its provisional ‘truth’ as a matter of science by how well this hypothesis meets criteria for 1) explanatory power for the diversity, commonalities, and contradictions of moral standards, 2) explanatory power for puzzles about moral behavior, 3) predictive power for moral intuitions, 4) universality, 5) no contradictions with known facts, and so forth.
Of course, provisional ...