There's no question that properly functioning human beings -- those that are not subject to a dysfunction or insanity -- have a sense of right and wrong. We perceive certain aims as good or bad, actions as right or wrong. We know that some actions and aims are permissable while others are prohibited, and properly so. It's also true that there is a great diversity of opinion on what exactly COUNTS as right or wrong actions and aims. All this is true whether or not one is religious (of whatever flavour) or not.
From a Christian religious point of view, this is easily enough explained. We are created in the image of God, and part of carrying God's image is that we perceive right and wrong. We have a conscience. So what's with the diversity? Well, Christianity holds that humankind is fallen. That is, we all -- by nature it seems -- prefer to be our own master. This rebellious streak has alienated us from our creator, and as a result, from the one who has designed the whole cosmos. No wonder, then, we have difficulty perceiving and agreeing on how to be human!
What's an atheist to say? By atheist lights, God is ruled out, so the source of our conscience must be explained naturalistically, which means that it must be an evolutionary adaptation. But if so, our moral intuitions lose the characteristics that would make them "moral." If my conscience is really just an evolutionary adaptation, there's no particular reason to think that it puts me in touch with anything like moral "truths". That is, what we might call our moral intuitions are simply emotive; there's nothing right or wrong about them. But if so, most of our moral discourse is puzzling. For certainly we debate about what the (morally) right thing to do is. Is it morally right to legalize the possession of marijuana? Is free market capitalism morally superior to communist socialism? We can and do debate these and other moral questions on the assumption that there is a correct answer. But if our conscience doesn't put us in touch with moral truth, what's the point in having the debate?
One might say the point is that we still have to live together, so we have to decide which system is best for us. But there's the rub. What do we mean by "best"? Is there any truth to the question whether any particular system is "best", even "best for us"? Again, probably not. At least, if there is a best, there's no reason to think that our conscience will put us in touch with the answer. We'll have to remain forever agnostic; or what is equivalent in moral reasoning, amoral.
In short, morals are deontological. They claim to provide a standard for human behavior. More, they claim to provide a standard that has the force of permission, obligation, prohibition, and so forth. But what sense can we make of these notions on atheistic grounds? I daresay none. The best we can hope for is prudence. I must not murder because, if I get caught, other people will do nasty things to me. But such a principle is hardly "moral."
But by Christian lights, our moral reasoning and quandary all make perfect sense. We reason morally because, as God's image-bearers, we have a sense of right and wrong. Right and wrong are determined by God's personality and intentions for the world he created. A deontological morality makes perfect sense here. And so does our muddledness. We misperceive or fail to apply what we know about morality because of our desire for autonomy, which clouds our moral judgment, which itself depends on a humble, thankful, and submissive attitude toward our creator.
