There are in our contemporary Western society two live options when it comes to worldviews - theism and naturalism (or materialism). When considering the adequacy of these two alternatives one of the things that needs to be addressed is the ethical (or more precisely, metaethical) implications of each.
Naturalistic ethics are beset with difficulties, not least of which is that it's very difficult to live consistently with naturalism, and it's especially difficult to live consistently with the ethical difficulties.
Here are five difficulties for ethics that follow from a naturalistic worldview:
1. No naturalistic account of morality can explain why human beings have dignity, rights, and worth.Where do any of these things come from in a purposeless universe?
2. No naturalistic ethics, which by its nature excludes ultimate accountability, can have any binding force. If there's no transcendent moral authority to hold us accountable how can there be a moral duty or obligation to do anything?
3. No naturalistic ethics can give a plausible explanation of what it means to say that a particular behavior is morally wrong.The word "wrong," when used in the moral sense, has no objective meaning. It can only refer to our subjective feelings about something.
4. No naturalistic ethics gives a satisfactory answer to the egoist who asks why he should care about the interests or well-being of other people. Why would it be morally wrong to only care about oneself and what's important to oneself?
5. All naturalistic ethics are at bottom subjective. There can be no objective moral duties if there’s no transcendent moral authority and no ultimate justice. In other words, naturalistic ethics is simply an expression of an individual's feelings, preferences, prejudices, etc. On naturalism ethics is simply a matter of individual taste.
Judeo-Christian ethics are a subset of what philosophers usually call Divine Command ethics (DCE). Based on theism, DCE has several advantages over all forms of naturalistic ethics:
1. Being rooted in a transcendent moral authority who is both omnibenevolent and omniscient, DCE gives us a basis for moral right and wrong beyond human reason or subjectivity. It gives us a non-arbitrary source of principles of moral right and wrong grounded in a transcendent, personal moral authority. In other words, it answers the question of the source of moral obligation and gives us a basis for both objective moral duties and moral absolutes.
2. DCE offers an answer to the egoist's question why it’d be wrong to just live for oneself and offers a basis for rejecting the ethic of might makes right.
3. DCE gives us a reason to believe that we're ultimately accountable for how we live.
4. Because theism assumes that we are created in the image of God and loved by God DCE gives us a basis for believing that human worth, dignity, and rights are not mere illusions or fictions but actually exist objectively and that justice will ultimately prevail in the world.
When people who doubt the existence of God make moral judgments, when they say that racism or sexism, for instance, are wrong, they should be asked what they're basing their judgment upon.
If they're pressed to answer, they may say something like they're wrong because these things harm people and it's wrong to harm people. But then they should be asked why harming people is wrong. Other animals do it to each other all the time, why is it wrong for humans to harm each other?
The naturalist will ultimately take refuge in something like the good of society or one's own individual self-interest, but why should an individual care about the good of society? Why are they wrong to not care at all about society? And why is it wrong to harm others if someone can get away with doing so with no accountability in this life or the next?
Eventually, the "why" questions come to an end with the naturalist's admission that things are wrong because he or she simply doesn't like them, but the likes and dislikes of another person are hardly reasons to think that some behavior is morally wrong. Why should anyone think that they should live according to what someone else likes or dislikes?
As in many other of life's ultimate questions in the matter of ethics naturalism turns out to be an inadequate worldview and vastly inferior, metaphysically, to theism, particularly Judeo-Christian theism.
Perhaps, the most frequently cited difficulty with DCE is something called the Euthyphro Dilemma and, although many critics of DCE are fond of it, it doesn't seem to be all that serious. For a three-part treatment of the Euthyphro Dilemma on VP go here, here, and here.