Having the 'divine judge' to 'help one keep oneself on the strai(gh)t and narrow' doesn't make god the source of the morality, or necessary to it. By the same token, the laws against murder, and punishment under those laws, do not define the morality or immorality of killing, they just enforce it using collective means. Society collectively (or the majority of individuals in it individually, or the leaders individually or collectively) determined/defined/believed that murder is wrong enough to warrant state action. Having murder be banned by law does not cause or define or create the immorality of murder, except to the extent that personal consequences of an action are morally relevant. Nor, in my mind, does social consensus NECESSARILY make actions to enforce a law moral. I consider drug laws immoral, because though drug use and sale may not always be moral, per se, they are less immoral than using force to prevent them. Use of force, even to enforce moral or legal rules, is a necessary evil, not a good, and has to be balanced morally against the acts they (actually) prevent.
By the same token, that 'god' judged killing as wrong in the bible doesn't necessarily create the immorality of killing, it just necessarily enforces it. Morality could exist through social definition of right and wrong, or as a part of the natural or supernatural universe separate from (or bound to - that isn't ruled out) the existence of a godhead, which may be accessed logically or empirically.
It could even be that morality is binding on a god, depending on your beliefs(priors?). (Eg. I believe morality is sufficiently separate from godhood that, even if god, by whatever name or definition, exists, his status as 'creator of the universe and of man' and his power to force his will on everyone would be insufficient basis for him to overrule the moral status of murder to say (for example) 'killing this baby is ok, I command it' - he could order this, but it would be wrong of him to do so. He would be morally culpable just like any other morally-conscious being. IOW, the biblical flood would have been an act of extreme evil, had it occured.)
To Jacob's point, I submit that the beliefs of the religious simply reflect the moral understanding of the social group the religious belong to. Fundamentalist morality reflects an social difference - a social group where the understanding of morality is different from that of social groups consising of the less fundamentalist churches. "Using drugs is bad" isn't lifted from the bible, it is a social norm which has been retrofitted onto Christian belief by some denominations. An even better example are the denominations which ban alcohol, despite Christ explicitly turning water to wine for his followers. Rationalization about 'it was grape juice, not wine' simply demonstrates how moral understanding is projected onto religion, rather than flowing from it. (See also the scrambling to justify belief that homosexuality isn't wrong while remaining Christian believers in a bible which is fairly explicit in saying the opposite, by more liberal denominations.)
God, say the religious fundamentalists, is the source of all morality; there can be no morality without a Judge who rewards and punishes. If we did not fear hell and yearn for heaven, then what would stop people from murdering each other left and right?
Suppose Omega makes a credible threat that if you ever step inside a bathroom between 7AM and 10AM in the morning, he'll kill you. Would you be panicked by the prospect of Omega withdrawing his threat? Would you cower in existential terror and cry: "If Omega withdraws his threat, then what's to keep me from going to the bathroom?" No; you'd probably be quite relieved at your increased opportunity to, ahem, relieve yourself.
Which is to say: The very fact that a religious person would be afraid of God withdrawing Its threat to punish them for committing murder, shows that they have a revulsion of murder which is independent of whether God punishes murder or not. If they had no sense that murder was wrong independently of divine retribution, the prospect of God not punishing murder would be no more existentially horrifying than the prospect of God not punishing sneezing.
If Overcoming Bias has any religious readers left, I say to you: it may be that you will someday lose your faith: and on that day, you will not lose all sense of moral direction. For if you fear the prospect of God not punishing some deed, that is a moral compass. You can plug that compass directly into your decision system and steer by it. You can simply not do whatever you are afraid God may not punish you for doing. The fear of losing a moral compass is itself a moral compass. Indeed, I suspect you are steering by that compass, and that you always have been. As Piers Anthony once said, "Only those with souls worry over whether or not they have them." s/soul/morality/ and the point carries.
You don't hear religious fundamentalists using the argument: "If we did not fear hell and yearn for heaven, then what would stop people from eating pork?" Yet by their assumptions - that we have no moral compass but divine reward and retribution - this argument should sound just as forceful as the other.
Even the notion that God threatens you with eternal hellfire, rather than cookies, piggybacks on a pre-existing negative value for hellfire. Consider the following, and ask which of these two philosophers is really the altruist, and which is really selfish?
Blank out the recommendations of these two philosophers, and you can see that the first philosopher is using strictly prosocial criteria to justify his recommendations; to him, what validates an argument for selfishness is showing that selfishness benefits everyone. The second philosopher appeals to strictly individual and hedonic criteria; to him, what validates an argument for altruism is showing that altruism benefits him as an individual: higher social status or more intense feelings of pleasure.
So which of these two is the actual altruist? Whichever one actually holds open doors for little old ladies.