Let's start with a relevant analogy: Science versus faith. The foundation of science, far more important than any particular discovery, is accountability: Any scientific claim must be verifiable. As Richard Feynman famously said,
The first principle [of science] is that you must not fool yourself - and you are the easiest person to fool.Science is the process of finding rational, consistent explanations for natural phenomena, explanations that can be written down and verified by others. Any fact, however trivial, that contradicts a scientific theory immediately requires that the theory be revised or rejected.
By contrast, faith-based explanations of natural phenomena (we are, of course, talking mainly about creationism and its relatives) have no accountability. They don't have to match the facts, they don't have to provide any deep insight, they don't have to be verifiable. Worst of all, history shows that faith-based explanations of nature are often motivated by politics and power, not a desire for knowledge.
Now back to morals.
Secular morality has rested on the solid foundation built by the Greek Rationalist (Plato, Socrates, Aristotle and their intellectual followers) for over 2,500 years. These amazing philosophers realized that morals had to start from a foundation that everyone could agree on, that is, an axiom that was plainly true. They selected happiness and improving the human condition as their axiom; who could possibly dispute that happiness and health are good, and suffering and pain are bad?
Based on this axiom, the Greek Rationalists built a set of moral principles, one that was based on sound logic, and that anyone could examine for flaws. And many did: The earliest ethical treatises have been discussed, dissected, and improved since they were first proposed. Yet even today, Aristotle's ethics stand as one of the greatest intellectual achievements of all time.
The key point here is that secular morality has accountability. You can't just make stuff up; new claims about secular morality must rest on the foundation of improving the human condition and must have a logical connection to that foundation. Furthermore, like the scientific method, secular claims about morality are open to scrutiny. If you make a claim about morality, you have to explain it clearly, show how it is derived from the foundation, and be willing to defend your position.
By contrast, religious morality is without foundation. If you believe morality comes from God, then you fall into trap that Plato discovered: What is the foundation of God's morality? How does God know what is good and what is bad? If you argue that God just knows, then you've admitted that there are things (like human happiness) that are axiomatic, and you're back to the secular position – you don't need God in the equation. If you argue that something is good because God says it's good, then God could say rape and murder are good, and they would be good, and the argument is circular; there is no foundation.
Those of faith claim their morality is inspired directly by God, but if that's true, then God is very confused. For example, He made numerous laws about how to treat slaves, but no laws prohibiting slavery. He made conflicting laws, and dietary laws that make no sense in today's modern world. He made laws that we have to prostate ourselves and praise His glory, a very odd thing for a supreme being to want.
And if that's not enough, religious morals quickly lose relevance as societies progress, yet they're frozen in time by the "inerrancy meme" – it asserts that the Bible is a perfect transcription of God's own words. Morality becomes cast in stone, and religions can't adapt as human society advances.
I discussed in a previous blog how churches claim to have the "lock" on morality, that without God, morality is impossible. In fact, just the opposite is true: Religious morals are inherently inferior to secular morals.