Reason is limited in normative ethics. Regardless, I don't think morality is something that comes out of some people sharing some common beliefs. In that sense, it'd be subject-given, or subjectivist, and based on their personal whims and desires. Morals actually are object-given, in a way that some objects are worth achieving on their own intrinsically. The purpose of moral discourse is to come to understanding of the metaphysics so we can establish an objective groundwork for ethics, that's based on simple object-given axioms. And from there-on, we can arrive at institutions like law that are based on historical conceptual growth through dialectics. But it all starts from an objective framework, independent of subjective thought.