The divine command theory
I'm not a big fan of the divine command theory, but I don't think it is as problematic is some people suppose.
The divine command theory is a theory of morality that says the moral law is based on God's commands. The major problem with it is that it falls victim to Euthyphro's dilemma. Is something good because God's commands it, or does God command it because it's good?
If God commands it because it's good, then goodness comes before the command. If goodness comes before the command, then the good cannot be based on the command. So divine command theorists can't take this horn of the dilemma.
If something is good simply because God commands it, that makes the moral law seem arbitrary. If God's commands aren't based on anything prior, then he could've commanded anything at all. The only reason we have the moral law as it is is because God artibrarily commanded it to be so.
That strikes most people as counter-intuitive. It's not hard to think of counter-intuitive results that follow from this horn of the dilemma. God could've commanded mother killing and father raping, and they would've been good. He could've forbidden kindness, generosity, and loyalty, and they would've been bad. But our intuition balks as such suggestions!
Why? This is the weakness I see in this sort of argument. If God has forbidden us to kill our mothers and rape our fathers, and if he has commanded us to be loyal, generous, and kind, then of course our intuition will balk at the suggestion that things be otherwise. We balk because things are not otherwise. We live in a universe where things are the way God has made them. We have moral intuitions that are consistent with God's commands. So naturally the suggestion that things be otherwise are going to be counter-intuitive. If things were otherwise, then we would likely not balk so much.
So the fact that the suggestion of killing our mothers is counter-intuitive is not a good argument against the divine command theory.
But what of the fact that God's commands are arbitrary? Now I don't grant that they are arbitrary, but let's assume they are. What difference does that make? Are they any less binding just because they happen to be arbitrary? If God is the ruler of the universe, then we're obligated to obey him whether his commands are arbitrary or not.
I suppose the fear is that if they are arbitrary, they are subject to change. We don't want them to change, and we don't want a fickle God. But can't they be arbitrary and consistent at the same time? Isn't it possible for God to make arbitrary moral laws and stick to them? If so, then why worry about God being fickle?