If religious ethics is true, then there can be no such thing as moral progress, because the moral principles accepted by primative people living in biblical times was perfect, which means it cannot be improved. Progress in General
Would you trust your child to a doctor that has read no medical text book that had been written in the last two thousand years?
If you needed a bridge built, would you consider the best bridge builder to be somebody who popped into this century after last working to help Caesar cross the Rhine River?
It seems unlikely.
It seems unwise.
The Possibility of Moral Progress
Yet, there are those who think that we should structure society according to moral principles and practice set down two thousand years ago, and ignore anything written or said since that time. Those ancient principles, they assert, were perfect. This means that nothing discovered since then can improve on those principles.
This is as dangerous as trusting your child to a doctor or your bridge to an engineer who thinks that nothing positive could have been discovered and no improvements made over the past two millennia.
Not a Relativist Argument
This is not an argument for common moral relativism -- a view with which I emphatically disagree. This view is willing to treat moral principles like medicine and engineering. The principles have not changed -- at least not much. However, our understanding of those principles has improved significantly over time. Over the course of that improvement, religion has been more of a hindrance than a help.
Morality vs. Law
Morality is concerned with organizing societies in ways that make the lives of its citizens better than they would have otherwise been.
Some may argue that this is the realm of law, and not morality. However, in the realm of law, we still have to ask, “What makes a law just or unjust? What laws should we have and what laws ought not to exist?" Ultimately, these are moral questions that cannot be answered without investigating the nature of justice and 'ought'.
The question then becomes, “Can we improve the ways in which we organize society to better benefit the people who live there?” The answer to this seems obvious. Just as we can improve health care, and improve on our engineering practices, as we gain information over time, we are also able to discover and put into place better ways of organizing our society and better moral principles to live by.
The Substance of Moral Progress
Improvement, of course, requires the ability to recognize which primative ideas were wrong and need to be abandoned. It requires the ability to make adjustments in what we believe is right and wrong.
For example, primative acceptance of slavery was a mistake. We need moral principles separating church and state in order to prevent the violent destruction in religious wars that emerge when state and church are mixed. A better society is one that treats women and men as political equals, gives members of the press freedom from political persecution, and requires that the accused be convicted by a jury of its peers before punishment is justified. Such a society respects the scientific method and the results that scientists come to -- results that have helped us fight starvation, disease, and the forces of nature.
All of these ideas -- ideas that did not occur to primative people (or the gods they invented) -- are ideas that now know make important contributions to creating a society in which everybody, on the whole, is better off.
I want to repeat, saying that moral progress is possible is not the same as saying that moral principles themselves change over time -- any more than the possibility of medical or engineering progress means that biology or physics has changed over time. It means that, because of our improved understanding of the universe, we can have better medical care, better engineering, and better moral systems, than primative tribes could have dreamed of.
It takes a vivid imagination to think that our contemporary moral principles can all be found in books written in the distant past. The case that our laws are grounded on religious text would have a lot more support if God had given Moses the 10 Amendments (also known as the Bill of Rights) rather than the commandments that are listed -- some of which are now widely regarded as unjust and unsuitable for a just society.
Why could God have not said, "Thou shalt not own another person or treat him as property?" Why could God not have said, "No person shall be subject to punishment unless first convicted by a unanimous vote by a jury of his peers?" Why did God not say, "No human shall rule over another as a Monarch or King, but only at the will of the people casting votes in a fair election.?"
God did not say these things because the people who invented God had not yet learned them. They had some moral rules right -- prohibitions on lying, murder, and theft. But they still had a lot to learn, as did the Gods they invented.
The Constitution of the United States could have been dictated by a benevolent God at the start of time. We could have had a Book of Monroe that identified the three parts of government and ways for keeping them in a system of checks and balances. Instead, it was “We the People of the United States, in Order to form a more perfect Union, establish Justice, insure domestic Tranquility, provide for the common defence, promote the general Welfare, and secure the Blessings of Liberty to ourselves and our Posterity,” who ordained and established this Constitution for the United State of America.
The authors of the Constitution were aware of the fact that they were merely human and subject to error. They knew that future generations would come up with new and better ideas. Therefore, they included a method for revising the Constitution and incorporating these improvements.
Summary
On the other hand, religious ethics simply denies the possibility of moral progress. They insist that the original rules were correct because they were handed down by God. That which is perfect when it begins cannot be improved. That which was handed down by God cannot be corrected by humans thinking up better ideas.
This assumption, that primative tribes knew the best rules for organizing society, is a very dangerous assumption to make -- as dangerous as trusting a child's medical care to primative shamen or having modern structures built using only those engineering principles accepted at the time of Caesar.
We will almost certainly pay a very high price in terms of human suffering if we insist on using primative rules written by substantially ignorant people long ago to organize a modern society.
The concept of moral progress is entirely at odds with the idea that these primative tribes had a perfect moral code.