If you cant bring yourself to kill someone on Gods orders because you cannot get over the idea that its wrong, then you are of necessity appealing to a higher moral standard than God (higher in the sense that it supercedes God, the way one court is higher than another). Never mind where this sense of wrongness comes from yourself, society, universal compassion, etc.; never mind that your moral take on the issue may actually be in error. The fact of the matter is, you are defying a direct imperative from your god by saying I disagree.
Plato & Kierkegaard
This question harkens back to a long-standing dilemma discussed by Plato. To paraphrase: Is it good because God says it is, or does God say it because it is good? Those who answer yes to the directive to murder fall squarely into the first category: If Gods telling me to do it, it must be okay, no matter what I personally may think of it. As for everyone else, the inescapable conclusion is that you feel there is an external moral code with which God could (theoretically) be out of alignment or at the very least, with which you yourself should not be out of alignment.
Now, Ive tried to be as ecumenical as possible here, but at this point I have to allow that pantheists may have trouble with this formulation, since they believe that there is nothing that is external to God; furthermore, some conceptions of divinity are non-personal, meaning that God cannot have desires or give commands.
Beyond that distinction, however, the fact remains that if murdering under the circumstances Ive described is wrong, and God has told you to murder, and you refuse for ethical reasons, then you must feel that the simple fact of Gods ordering it has not suddenly made it Good. Ergo, you feel that there is an external Good to which even God adheres to, or does not adhere to, as God chooses.
Again, I should stress that we are not talking about Cosmic Certainties here you could always be quite wrong in your belief that murder would still be evil even if God required it of you. The point being explored here is, what are the consequences and corollaries of the beliefs you hold and the decisions you make, or would make?
For those Western monotheists who are still clamoring that God would never make such demands of them, I must humbly point to the example of Abraham and Isaac. When I was in college, I studied Kierkegaards Fear and Trembling, in which he argues that by sacrificing Isaac, Abraham makes a leap of faith in God so profound that its not even possible for most people, and therefore Abraham is to be praised and held in highest esteem for his decision.
To his credit, Kierkegaard struggled with this issue a great deal before coming to this conclusion which is, Im afraid to say, a lot more thought than I gave the matter when I went along with the class and agreed that, yes, Abraham was a pretty amazing fellow.
Abraham as a Yes-Man
Recently, I had occasion to reevaluate my opinion on the issue, and I came to a very different conclusion. For Abraham is nothing less than that person who unthinkingly says Yes, Lord when told to murder another human being. To be sure, the Bible encourages us to overlook that fact, because the story starts out by clearly stating, God put Abraham to the test.
In a way, its almost like a Hitchcock movie: the audience knows that its a test, so the suspense lies in working up to that awful moment when Abraham picks up the knife. Will he do it? Can he do it? we ask ourselves with a mixture of horror and admiration. And sure enough, he does he passes the test, we all sigh with relief, and Abraham gets blessed and lives happily ever after, more or less.
But Abraham didnt know it was a test.
We tend to forget this, but from his perspective, he was going out to kill Isaac, and tomorrow hed have to figure out what to tell Sarah when he got back home. Once we incorporate this into our reading of the text, how can we possibly feel anything but horror at what he was prepared to do? Here is a man who was prepared to murder his own child, and the Bible makes no mention of him disputing the order, or even that he felt very upset about it. Perhaps the historical Abraham would have indeed done so, but the biblical Abraham does not and this is the example which the Bible holds up as praiseworthy.
Think about it: Nowadays, any parent who claimed she killed her child because God told her to would be thrown into jail, or into a mental institution the only question would be in deciding which (although in Texas the choice is more between life in prison and execution, as demonstrated by the case of Andrea Yates). I challenge anybody to find one person who would hear about it and exclaim, Wow, I wish I had that much faith! People who would not kill even a stranger on Gods say-so cannot fathom the sheer mindless obedience it would take to kill ones own child. I know I cant.

