All Ethical Systems are Faith-Based

Call it divine law. Call it natural law. Call it godless Objectivism. No matter. It's all faith-based.

Sure, you can develop a system of ethics "rationally," based on your axioms and definitions. Sure, your conclusions are logical. They're still contained in those axioms and definitions.

Those axioms and definitions aren't so self-evident to everybody else. You accept them on faith or you reject them. The Great God Natural Law won't help you.