Introduction
One of the most important concepts to be comprehended by we humans is morality. This importance derives not only from the fact that we are intelligent beings, but also from the fact that we are social beings. And although there is perhaps universal agreement on its practical value, there is substantial disagreement with respect to its theoretical nature.
For instance, one of the hallmarks of Christian thought is absolute objective morality. That is to say that there are certain moral "laws", which are unchanging with respect to situational variance and are universally applicable. This is a comforting position, since it reflects our social need for safety, security, accountability and justice. And because humans and therefore the constructs created thereby are imperfect it is desirable to hold some notion of ultimate and final justice, which is inescapable. Understandably, then, it is a common complaint of the religiously minded that if one gives up any notion of the supernatural, then one must also give up this view of morality. But this is undesirable because it leaves us with moral relativism. In Dostoevsky's The Brothers Karamazov Ivan Karamazov laments:
"If God does not exist, then everything is permitted."
For the purposes of this post, let us forget that this is an argument from consequences and therefore fails as an argument for the existence of God. Instead, let us consider whether the accusation is even true. More specifically, it will be useful to consider the more legitimate argument from morality. The question at hand, therefore, will be: Can morality be absolute and objective in any meaningful sense if God does not exist?
The Moral Argument
One of the more common arguments employed for the existence of God is the Moral Argument. It's basic form is usually stated as follows:
(i) If God did not exist, then objective moral values and duties would not exist.
(ii) Objective moral values and duties do exist.
(iii) Therefore, God exists.
(Moreland J.P., Craig William Lane. Philosophical Foundations for a Christian Worldview. p 495)
Again, I am going to assume that (ii) is true, but question the truth of (i).
Observe that (i) is logically equivalent to (i'): If Morality exists, then God exists. (Here I shall use Morality as an abbreviation for objective moral values and duties). So, the first premise states that the existence of God is a necessary condition for Morality. If this is false, then it must be shown that (Morality exists) and (God does not exist) is consistent and does not produce a contradiction.
In defense of (i) it is often phrased in terms of "laws" and argued that laws require a Lawgiver. One site puts the matter this way:
"There is nothing out there in the physical world that makes moral facts true.
This is because moral facts aren’t descriptive, they’re prescriptive; moral facts have the form of commands...
There are some things that can’t exist unless something else exists along with them. There can’t be something that is being carried unless there is something else that is carrying it. There can’t be something that is popular unless there are lots of people that like it.
Commands are like this; commands can’t exist without something else existing that commanded them.
The moral argument seeks to exploit this fact; If moral facts are a kind a command, the moral argument asks, then who commanded morality? "(http://www.existence-of-god.com/moral-argument.html)
The obvious question is: Must Morality be thought of in terms of commands? It seems quite obvious that this is not necessary, since the maxim, You should not murder can always be stated instead as It is not good to murder. At this point, however, we need an understanding of the word "good". Furthermore, even if we can conclude that Morality need not inherently exist in the form of commands, this would not prove God does not exist. But remember, the objective here is to explore whether or not (i) is a true implication.
The Euthyphro Dilemma
Now, from the Christian perspective "goodness" must be identified with God's nature. The necessity of this position arises from the well known Euthyphro Dilemma, which asks:
Is something good/Moral because God commands it or does God command said something because it is good/Moral?
The dilemma comes from the fact that if the first disjunct is the case, then Morality is arbitrary and reduces to might makes right. Presumably, then, God could have commanded that, say, men shall be permitted to rape a woman from 6pm to 7pm every weekday with amnesty. Thus, since this is clearly an untenable position one might opt for the second disjunct. But should this be the case, then our work here is done, since it admits to an objective standard apart from God and then one may easily ask why God is necessary at all.
Because of this, the theist is forced to either accept one of these undesirable positions or to find a way out of the dilemma. This is precisely what most theists attempt by arguing that there is a third option. They claim that God's very nature supplies the absolute standard and that any and every command issued by God must/will be consistent with "His" immutable and necessary nature. Presumably, then, something like murder is wrong not so much because it results in a dead human (since that happens in many other ways), but because the act of murdering arises from hatred and a destruction, which are qualities that conflict with those found in God. Of course one could also argue that God values human life and so taking it "without just cause" is wrong. So, objective good is synonymous with God's nature and any value humans have is derivative in nature. That is, X has value if and only if God values X. But God values X if and only if X exemplifies qualities consistent with "His" nature. Therefore, X has value if and only if X exemplifies qualities consistent with God's nature.
Similarly, the theist must argue that Y is good/Moral if and only if Y exhibits qualities which coincide with God's nature. But does this really solve the problem? After all, how does one understand the nature of God? Any sophisticated theist will agree that this nature must be necessary, since if not, then it just so happens that God is the way "He" is and so could have been different. In other words, God's nature is accidental and one might rightly wonder how an accidental objective standard is an improvement on God arbitrarily deciding what is moral. In fact, the generally accepted definition of God as the being than which no greater can be conceived rules out this possibility unless we permit that there could be various variations on God's nature but that no one of these is "greater" than any other. But this (possibility?) is inconsequential to our investigations.
A Shot to the Foot?
So the theist concedes that there are ways of conceiving God and "His" nature which are "greater" than others, that God necessarily has the greatest possible nature. Now admittedly, we need not be able (and perhaps are not able) to fully formulate what this nature would be, but we are able to reason about certain qualities that definitely do belong to this nature. We say that this nature is perfect, since, again, it would not be appropriate to define the notion of God any other way. But if we can understand the nature of God, then we can understand morality. In going about this theory we implicitly recognize a set of values and characteristics we recognize as necessarily good and that God, should "He" exist, must possess these necessarily. But then it is really these values that are the standard and one has to wonder why they need to be made into characteristics of personal being? That is, how does evoking the existence of a personal being whose nature is characterized by these values make Morality any more real or substantiated? It seems that the theist is multiplying entities beyond necessity to account for morality in defiance of Ockham's razor.
Conclusion
Therefore, since the set of values and/or properties that describe God's nature can be understood independently of their being instantiated in a person it seems that there can indeed be Morality in the absence of God. We then recognize that if a person can exemplify these qualities, then that person will be a "good" person. Again, this does not mean that God does not exist, but it does mean that the moral argument fails as a proof. More than that, it shows that theism is not even necessarily the best way to account for Morality and so cannot be turned into a strong inductive argument or probabilistic argument.
What's the Real Issue?
Despite the inadequacies of the moral argument, it nevertheless continues to be a very persuasive argument. This is most likely due to strong psychological factors, which appeal to the strong desire for justice found in nearly all humans. It is very difficult for us to accept that some fiend could "get away with murder" or some other terrible crime and not be held accountable. This naturally leads to desire and hence posit the existence of a divine arbiter of justice whose judgment cannot be averted or escaped. And if there is no such being, then one understandably wonders what is the motivation for being good! This is a complicated issue to be sure, but a few reasons are
(1) We need others as social beings.
(2) We may be punished by our peers.
(3) We have the ability to empathize with others.
(4) Humans rightly seek what has value and being good has value.
There are certainly more reasons, but I think this is a decent list. The real issue then seems to be the potential consequences of not believing in God. But as mentioned above, this is a fallacious way to argue for the actual existence of God. At the very least we should be good because we understand what "goodness" is and we desire to bring that into existence. Should we all decide that it is not worth it, then nature will eliminate us and something else will take our place.