I think that the divine command theory of morality suffers from a number of problems that, cumulatively, render it fatally flawed:
Does God exist?
A serious objection to the divine command theory of morality is that it assumes God’s existence. If God’s existence can be questioned, then the argument for a divine command theory of morality is undermined. In fact, I would contend that not only are we entitled to doubt the existence of God, but that we can go much further and argue that the case for the existence of God (with all of its very particular properties and desires), is very weak – although I won't elaborate upon that any further here.
If God doesn’t exist, then we have no mandate to follow the moral rules attributed to God for that reason alone. We might still decide to incorporate some of them into our moral framework, but they must stand or fall upon their own merits, not because they are supposed to be commands issued by God.
What makes God’s commands morally good?
If, for the sake of argument, we assume that God exists, then we are entitled to ask why the morality commanded by God is good. When considering this question, we might usefully refer to Plato’s famous Euthyphro dilemma: is what is moral commanded by God because it is moral, or is it moral because it is commanded by God?
In the former case, then we can just help ourselves to this morality without reference to God at all, as it makes God just the passer-on of a morality that exists independently of him. It also leads to a number of further questions that the theist needs to answer. For example, where did this morality come from in the first place, if not from God? Did it exist before the universe? If so, does it make any sense to conceive of some abstract or idealised concept of morality existing before the universe? If this morality is somehow independent of God, then how does God know that it is necessarily good, if he has no absolute moral yardstick against which to measure it?
Alternatively, the theist may take the second option. In this case, God could have commanded murder to be morally good, for example, and it would be so - since the command comes from God. In this case, the theist then has two further options. They may just bite the bullet and accept that murder would indeed have been morally good had God commanded it so. However, few are willing to subscribe to this view, as it contradicts our most basic concepts of what constitutes moral behaviour. On the other hand, the theist may contend that God would never have commanded murder to be a moral rule as God, being perfectly good, would only command what is good. However, this is just circular reasoning, and doesn’t deal with the dilemma, as we can rephrase it to deal with this objection i.e. is God good because to be good is just to be whatever God is, or is God good because God has all the properties of goodness? We are back in the same situation again with goodness either being arbitrary, or existing independently of God.
Why should we obey God?
Again, if for the sake of argument we assume God’s existence, then why should we obey God’s commands anyway? If God was to command us to torture and murder others, then would we be obligated to obey such commands, even though they go against our common moral sense?
Of course, the theist may contend that God would not command us to do such things, as God is perfectly good. However, there are at least two problems with this reasoning. Firstly, there are plenty of examples in the Bible of moral atrocities supposedly being commanded by God, so the precedent clearly exists. Furthermore, some of the moral rules attributed to God would seem according to our common moral standards to be cruel and disproportionate in that they specify a penalty of death for such supposed crimes as blasphemy, picking up sticks on the Sabbath, being a witch, and talking back to one’s parents.
Of course, some Christians might object that the New Testament gives a far kinder message, as preached by Jesus, and describes the new covenant between God and man. However, the New Testament still contains various odious rules and strictures, a command to still obey the rules of the Old Testament, as well as the introduction of the concept of eternal punishment for a variety of supposed sins. Moreover, in some Christian worldviews, the avoidance of hell comes by accepting Jesus as one's saviour - which therefore bars entry to heaven to all those who existed before Jesus lived, who don't hear his message for any other reason, or who have heard his message but have chosen to reject it in favour of some other belief system or of none. Moreover, the whole concept of the New Testament preaching a kinder message implies that God's personality or teachings have changed from those described in the Old Testament, or that he has changed his mind. But surely this cannot be so, as this would imply some sort of moral development or improvement on God's part, but he is by definition omniscient, omnipotent, and morally perfect. As such, how can he improve, and for what reason could he ever change his mind, since he already knows all there is to know?
Secondly, how can we ever know that something is good just because it is commanded by God, since we can never know that God is perfectly good? We cannot take God’s word for this, as it merely begs the question. And just defining God as perfectly good doesn’t settle the matter either, as I would contend that God’s existence and characteristics are synthetic propositions, not analytic ones, as we are dealing with aspects of the real world rather than just formal logic.
Furthermore, if somebody alleges that God has given them some moral command or other, or detailed a list of commands that we should all follow, then this too is highly problematic. How are we to know that this person is not deluded or lying? Moreover, assuming that the person in question truly believes that God has given them this moral command, then how can they themselves ever know that they were not just imagining it? Furthermore, even if they did actually receive some genuine communication, how can they or we ever know that this communication emanated from God, and not from some other entity – supernatural or otherwise?
For the foregoing reasons, I don’t think that anyone is entitled to evade moral responsibility for their actions by arguing that they are merely following a command from God, even if this were actually true.
What are God’s commands?
The moral and ethical guidelines in the Bible are often contradictory, and are open to multiple interpretations. So, how are we to determine exactly what morality is espoused therein? In light of this, I think that we might also ask why such supposedly important messages for humanity were not communicated in a clear and unambiguous fashion - one that is not open to multiple and often conflicting interpretations?
Of the moral guidelines that are more clearly expressed in the Bible, some deal with matters that would seem to be unimportant or neutral when it comes to a moral life. For example, rules to not eat shellfish, and to not wear clothes of mixed fibres.
Theists might attempt to gloss over the multiple inconsistencies in God’s moral law, as detailed in the Bible, and interpret it in order to render it more agreeable to our current moral sensibilities. However, if we decide to ignore or interpret certain of God’s moral rules (killing blasphemers, Sabbath breakers, witches, disobedient children; not eating shellfish, and not wearing mixed-fibre clothes etc.), but to follow other rules, then we have either made an arbitrary choice or else, more probably, we are making our choice based upon some other moral yardstick that is independent of the Bible. If it is the former, then it would seem to be a rather unreliable way to build a moral framework. If the latter case, then we might as well reason our way to this independent morality without reference to the Bible at all.
Are God’s rules necessary for a moral society?
One might argue that, even if we doubt God’s existence, society should still adhere to religious morality, as it will lead to greater moral health. However, it is rather conspicuous that many societies have or have had ethical systems that are not based upon some divine command theory, without them having any consequent morally bankruptcy. For example, the Ancient Greeks had a very well developed secular ethical system (they condoned slavery, but then so did Christian societies). Even though the Greeks had their own gods, these Gods apparently did not concern themselves with dictating moral laws.
Further, there is very good empirical data that shows a strong positive correlation between a society’s level of religiosity and the prevalence of all sorts of ills – crime, illiteracy, mortality rates etc. For example, many Western European societies are amongst the least religious in the World, but they can be seen to have a good moral health by almost all of the relevant markers. This doesn't necessarily imply a causal relationship, but it does undermine the theory that a society’s moral health is dependent upon it being religious.
Some theists argue that modern Western society is in moral decline, and correlate this with an increasing lack of religiosity. However, this is a fallacious argument. By almost any marker, Western societies are more moral than they ever were when they were more religious. They are freer, more equal, less violent, more compassionate, and so on. What the theists are doing when they make this type of argument is to confuse such societal tendencies as greater consumerism (which I would argue can be morally negative, neutral, or positive, depending upon the specifics), with a moral decay.
The theist may also assert that atheists or secular societies that they would consider to actually be moral are only so because they are living off the moral capital built up by a previous religious tradition. However, this argument seems to be an entirely ad hoc one, with no good supporting evidence ever being produced.
Who is the more moral?
We might reasonably ask who the more moral person is. The one who acts morally out of a selfless desire to treat others decently and compassionately, or the theist who is doing it in blind adherence to divine laws, or for prudential reasons, in order to gain a reward, and avoid a punishment from God?
Where does morality come from?
So, if morality doesn’t come from God, then where does it come from? I think that we have an innate sense of morality, and that this is derived from our evolutionary heritage. Our cultures and intellects have given us additional moral drivers, and modified existing ones, but I think that the roots of our morality are evolutionary. When our primitive ancestors started to form groups, their chances of survival were increased by acting in certain cooperative ways, and decreased by acting in others. Clearly, those who acted in those ways conducive to survival were more likely have offspring and to pass on their genes. Hence, tendencies towards such things as reciprocal altruism were selected for by evolution.
For example, the so-called Golden Rule clearly has a survival advantage for each member in a group if all group members adhere to it. In fact, it has been demonstrated in game theory that the principle that gives the best result for individual group members is one in which a member will initially cooperate with another member, but will henceforth copy the last action of the other member in a tit-for-tat fashion – either cooperating or not. The theory behind this is known as the Prisoner’s Dilemma. Lo and behold, examples of this type of behaviour are indeed witnessed in nature, and can quite clearly be seen to be precursors to our own morality.
That our innate morality is based upon our evolutionary heritage doesn’t mean that we shouldn’t seek to improve upon it. Science helps to explain what is the case, but not what ought to be the case. For this, we need to apply the methods of reason.
Can we have a secular morality?
If we are to dispense with religious morality, then what can we put in its place? Three major types of secular morality have been devised: Virtue Ethics, Kantian Ethics, and Utilitarianism. Each takes a different approach - emphasising virtue and flourishing, duty, and consequences of actions respectively, and each has its own strengths and weaknesses. Perhaps none is sufficient to take as a complete moral framework, so we may need to attempt to combine the best aspects of each in a way that doesn’t lead to contradictions and internal inconsistencies.
One big advantage that all of these secular moral systems have over the divine command theory is that none inherently entails a dogmatic and blind adherence to its moral strictures. Each offers a set of moral objectives or meta-rules but, as they were arrived at by means of evidence, reason, and reflection, they are theoretically open to revision and improvement. By contrast, divine commands are intrinsically dogmatic, since they were supposedly handed down by God, and they are thus strongly resistant to change. The result of this is that such moralities still incorporate many ancient rules that reasoned analysis would now class as either morally neutral (e.g. eating shellfish), or as unenlightened and bad (such as enshrining the inequality of women).
Furthermore, in light of the previously discussed flaws with the divine command theory of morality, I think that stipulating death for victimless crimes like the breaking of trivial ad hoc rules or for professing unbelief in God is in itself immoral. So, I would argue that for these reasons alone any of the secular moralities mentioned above is better than the divine command theory.
I would argue that some of the supposedly divine moral commands are merely parasitic upon our innate sense of morality, whilst others are at best irrelevant to a good morality and, at worst, in direct opposition to it.
I would further argue that the case for a divine command theory of morality is rendered fatally flawed because God’s existence is in clear doubt, because any such system of morality would either be arbitrary or independent of any God, because we should not just blindly follows such rules, and because the rules are ambiguous and inconsistent anyway.
I don’t think that any absolute and true divine system of morality exists (or any other absolute moral system, for that matter), so we don’t have the misplaced certainty of the theist. Instead, we need to build upon our innate sense of morality by devising a secular morality through the investigation of evidence and the application of reason. This task will not be easy, and much more work needs to be done, but I think that this is the best way forward in the quest for a good morality, as morality does not depend upon God.