Enter presuppositional apologetics. Instead of being satisfied that people can be moral without needing to account for morality, that morality can only begin with a sufficient grounding. So while one might believe that lying is wrong, by what standard can they justify it? To the apologist any valid justification has to be through God.
The alternative is subjectivism, without something universal to base a standard of morality on, it comes down to the individual to ultimately decide their own right and wrong. More on this is a future post, but for now let's suppose that is indeed the case. If God is the only way of bringing in an absolute standard, then what's the standard?
Again consider the case of lying, the apologist could say that God dictated lying is wrong and that's the end of that. But why does God consider lying wrong? Is there something inherently wrong with lying that displeases God? If so, then why is God displeased? Or is it that God makes the rules so whatever God says goes? If so then would lying be right if God dictated it?
This is The Euthyphro Dilemma, which can be stated as:
Is it pious because it is loved by the gods, or loved by the gods because it is pious?So for the question of whether lying is wrong, does God consider lying wrong because God says it's wrong, or does God say it's wrong because it is wrong? The dilemma leaves two unfavourable positions: morality either becomes arbitrary or a question external to the gods themselves.
Choice 1: arbitrary morality
If what the gods say goes, then it's necessarily arbitrary. Is murder wrong only because God says so? Then if God says murder is right then it's right. Torturing babies? on the whims of the deity the moral status hangs. Stealing from others is perfectly fine as long as God says so.
I can hear the apologist's objections already, it's not in God's nature to desire any of those things. God says murder is wrong because he's good and knows that murder is wrong. And this leads straight to choice 2.
Choice 2: circular morality
If it's in God's nature, then by what standard can it be said to be good? It may be in God's nature that he thinks murder wrong but that says nothing of whether something is right or wrong. If God's nature is perfectly permissive of murder then this mode of thinking would just as well label it good. In other words, if God's nature is good and good is defined by what God says then we hit a point of circularity.
The alternative is to define the terms external to the will of God. That God's nature is good because he embodies as standard for what is good that must be separate from what God is. This line of thinking puts the question of morality external to the gods and thus we don't need God in order for there to be right and wrong.
Now to consider the premise of an apologist accepting this problem (a really long shot) and instead turns it to facilitation. Yes there is a right and wrong, but it takes God to tell us what they are. The universals themselves may exist but as individuals we need God to recognise them.
Yet how could we recognise what is good without a conception of what makes good to begin with? If there is a god out there then how can we be sure that what the god says is good is actually good? Can a Muslim who believes in the divine revelation of Allah be any less justified in right and wrong than a Christian who believes in the divine revelation of Yahweh?
While the apologist might object that the Muslim belief is not consistent while the Christian belief is, it misses the point of the exercise. The right morality just happens to be the one the apologist grew up with. Talk about subjective!
What the Euthyphro Dilemma demonstrates is that there's no justification in appealing to gods in issues of morality. To argue otherwise is to argue that morality is merely arbitrary or fall into circular reasoning.
 - http://en.wikipedia.org/wiki/Euthyphro_dilemma
 - From William Lane Craig