They may be ultimately arbitrary, but until you come up with a final conclusive objective ethics, proven metaphysically beyond questioning, the rest of us have

They may be ultimately arbitrary, but until you come up with a final conclusive objective ethics, proven metaphysically beyond questioning, the rest of us have to make actual decisions today. The UN, as a collective body, defines various normative concepts, e.g., by defining "human rights." If you have issues with them, you join the proverbial mailing list and state your case.