Theists often maintain that a belief in God is essential for a moral or ethical life. One example of this argument appears at the Christian Apologetics website. John Quinley wrote this excellent rebuttal to the arguments there, and gave me permission to post it here. For the complete statement of the original article, go to the CARM website.  --Richard PackhamCARM: Atheists' morals are not absolute.
JQ: This is true of everyone, even Christians. Case in point: most Christians would consider it wrong to murder children, but according to the Bible, God repeatedly committed this sin, murdering the first born of every Egyptian household, murdering all of the children alive during the Noah Flood, murdering 42 kids for making fun of a prophet. How many Christians would consider God a sinner?
CARM: They do not have a codified set of moral laws by which right and wrong are judged.
JQ: Neither do Christians. Christians will claim the Bible is their codified set of morals, yet they ignore the vast majority of rules laid out for them in the Bible. Most Christians would not stone the children to death for dishonoring their parents.
CARM: This can be a problem as the norms of society shift and the ethics shift with them. In one century abortion is wrong. In another, it is right. Well, is it or isn't it right? If there is a God, killing the unborn is wrong.
JQ: Since, according to the Bible, God has no problem killing children, it does not follow that he would have a problem with abortion, and there are many pro-choice Christians. As far as the norms of society shifting causing a shift in ethics, does anyone remember the witch trials in Salem? Since, according to the Bible, witches should be killed, is CARM going to attempt to make it legal to kill witches? Will the members of CARM pick up the torch and stand up for their absolute, unchanging values?
CARM: If there is no God, then who cares? If it serves the best interest of society and the individual, then kill.
JQ: You mean like war? Surely members of CARM are not implying that Christians never kill.
CARM: This can be likened to something I call, "experimental ethics." In other words, whatever works best is right. Society experiments with ethical behavior to determine which set of rules works best.
JQ: "Evolutionary ethics" is perhaps a better name, and it is how most ethical systems come about.
CARM: There are potential dangers in this kind of ethical system. If a totalitarian political system is instituted and a mandate is issued to kill all dissenters, or Christians, or mentally ill, what is to prevent the atheist from joining forces with the majority system and support the killings?
JQ: This is a straw-man argument, and not a very good one. If atheists were inclined to join with the majority if it served our interests, then we would be confessing Christians. If I'm not mistaken, six million Jews were killed while their fellow human beings (almost all of which were Christian) watched. This issue has little to do with being a theist or a non-theist. Most people, theists and non-theists, go with the majority and are conformist.
CARM: If it serves his self-interests, why not?
JQ: Empathy, compassion.
CARM: But, to be fair, just because someone has an absolute ethical system based upon the Bible is no guarantee that he will not also join forces for the killings.
JQ: Are we not forgetting that the Bible condones genocide on multiple occasions? And let us not forget the Inquisition, the burning of witches, the crusades. Let him who is without sin cast the first stone.
CARM: But the issue is the base and ramifications of that base. Beliefs affect behavior. That is why belief systems are so important and absolutes are so necessary. A boat adrift without an anchor soon crashes into the rocks.
JQ: Let me see - 150 years ago, Christians owned slaves. 400 years ago, Christian burned heretics. Even today, some Christians bash homosexuals and relegate women to a lower state. And yet some don't. If Christian values are so absolute, how come there is such a variation of values amongst differant Christian groups?
CARM: The Bible teaches love, patience, and seeking the welfare of others even when it might harm the Christian; in this the ten commandments are a summary.
JQ: CARM has a differnt Bible than I have, or CARM has simply cut out most of it and thrown it away.
CARM: In contrast, the atheists' presuppositions must be evolutionary. Since evolution teaches that life is the product of purely natural and utilitarian properties of our world, survival of the fittest, natural selection, and equating humans to animals as a species are the ontological basis for our existence and living. With this the value of man is lowered.
JQ: This does not follow, and in fact, the opposite is true. It is true that humans are no longer the center of the Universe, but this conclusion is based on practical reasons, i.e. it is demonstrable that we are not the center of the universe. What we have learned in our increasing understanding of how we got here is that all life (including ours) exists in a state of balance and is very interrelated. Instead of demeaning life, this fact exalts life and helps us to understand how precious and how delicate it is. To the atheist, if we were to mess up the planet, we would have to fix it. There would be no one to save us.
CARM: In contrast, it is a very high calling to treat people properly who also are made in the image of God.
JQ: This statement has no meaning, and Christians themselves cannot even decide on what it means. What does it mean to be made in the image of God? Ask a million Christians, get a million answers.
CARM: Basically, I do not see how the atheist could claim any moral absolutes at all.
JQ: The real question is "Why do Christians claim moral absolutes when it is painfully clear that they have no idea just what those moral absolutes are?"
CARM: To an atheist, ethics must be variable and evolving. This could be good or bad.
JQ: If they are bad, then they will be selected out of civilization. I.e. destroying the Earth is bad, preserving it good. Of course, we try to reason these ethics out, since it is sometimes difficult to undo a system if one travels down the wrong path (i.e. fix the Earth after ruining it).
CARM: But, given human nature being what it is, I'll opt for the moral absolutes -- based on God's word.
JQ: You mean based on the 0.01% of it you actually practice.