My preferred metaethical starting point is to gather data about human, and more broadly animal, behavior. Frans de Waal is a leading primate biologist who teaches at Emory University. In the embedded video, he presents the concept of reciprocal altruism that he observed in his primate studies.
Reciprocal altruism is congruent with the Golden Rule, a basic ethical principle taught by all of the world’s major religions. That congruence is unsurprising. If there is a god who created the cosmos (and I do believe that this creator exists), then this god would have concern for all humans, seek to be in relationship with all, and try to communicate the same guidance for flourishing to all.
Alternatively, reciprocal altruism does not presume or require God's existence. The path to flourishing is discoverable by observing life and understanding how other species, closely related to ours, have flourished.
In any case, reciprocal altruism is objective without claiming to be the ultimate truth, i.e., in time humans may develop even better understandings of behavior and the path to flourishing/happiness.
Reciprocal altruism is also universal, at least for humans and a number of other animal species. This connectivity emphasizes the interconnectedness of life and the dependence of human flourishing on the well-being of the earth, perhaps ultimately on the well-being of the cosmos.
Finally, reciprocal altruism is not an absolute principle but a heuristic for shaping behavior conducive to flourishing/happiness. That is, in a given moment or instance a selfish act may be more imperative than an act of reciprocal altruism, e.g., a mother putting on her own oxygen mask before putting on her baby’s mask in a depressurized plane is actually in the best interest of both mother and child.
The thematic thread of flourishing/happiness that runs throughout this analysis rests upon a bedrock observation: humans, like other animals, almost always choose life over a death. Exceptions are notable because they are exceptions, e.g., a parent sacrificing his/her life to save a child’s life or a person with a terminal disease, intense suffering, and very little quality of life choosing death instead of more suffering. As with the concept of reciprocal altruism, this theme coheres well with a Creator giving life but does not necessitate that belief.
In sum, right is generally that which promotes the flourishing/happiness of life. Reciprocal altruism describes the broad outlines of what is right, i.e., that which promotes the flourishing/happiness of life. One can derive the rest of ethics – whether virtues such as honesty or courage, how to resolve ethical dilemmas when forced to choose between two goods or two evils, etc. – from those two metaethical principles.
Tangentially, empathy – community, loving relationships – along with an innate desire to preserve life motivates people to engage in reciprocal altruism. This concept figured prominently in the video, but often receives little attention from ethicists. The continuing need to relieve U.S. Navy commanding officers for causes related to personal misconduct suggest the importance of cultivating empathy and of being in healthy, loving relationships and community.
Shifting the metaethical discussion from the realm of revelation makes discourse truly possible without precluding people for whom revelation is definitive from participating. Shifting the metaethical discussion from the supposed realm of pure reason acknowledges that human thinking is contingent upon experience and the thinker’s position within time/history.
Grounding metaethical discourse in observable behavior allows for revision as new data becomes available yet establishes a discourse that, for humans, is both universal and objective in the present.