I disagree with this strongly. Moral law exists quite apart from any concept of God. It simply isn’t handed down from on high, for non-believers.
Agree with branwyn-says. It is not impossible to have moral laws without a God. The premise that guilt is sin’s only alternative is flawed.
I’m not saying, and I’m quite sure that James Sire (the author of the quote) wasn’t saying either, that non-believers have no moral code, or are unable to act morally. Nearly all non-believers manifestly do have a sense of right and wrong, and many try very sincerely to behave in a moral and compassionate way. Sometimes they even do so in ways that put believers to shame.
The point is that apart from divine authority there is no sound argument for acting morally. Because if God does not exist and our existence is purely a matter of chance, then moral impulses are either a result of chemical reactions in our brains that serve a purely evolutionary purpose (in which case it isn’t actually bad for an individual to go against those imperatives, just potentially ill-advised) or else moral values are a construct imposed on us by our upbringing, our culture and our society (in which case we we are in no position to judge the moral values or actions of any other individual, culture or society when they happen to conflict with our own — so we cannot call honor killing or concentration camps evil, only distasteful to our particular moral aesthetic).
Now obviously very few non-believers actually think their morals are just an accident of biology or something imposed on them by society — because deep down, we know our sense of right and wrong is more real and objective than that. All human beings possess at least some innate sense of morality, regardless of our intellectual or spiritual beliefs (which is the gist of Paul’s argument in Romans 2:12-15). We do what we believe is right because we really feel that it is the objective and not merely subjective right thing to do, and when we do something we know in our hearts to be wrong, it causes us to feel guilty. That is true whether we accept the premise that God exists or not.
However, when a non-believer breaks the moral law and feels guilt for it, there is no logical answer in her philosophy to why the guilt she feels is real, and not merely a biological illusion or a cultural artifact. Nor is there any clear answer as to what she can do to alleviate her guilt. That is the point of what Sire is saying.
If “doing wrong” is merely a matter of resisting your biological impulses or going against the rules of society, then there is no reason to feel guilty for doing so as long as you can rationalize it. But the fact remains that even if we can come up with arguments to justify our “wrong” behaviour, even if we try in some way to compensate by doing a corresponding “right”, we often still feel guilty. And there is no clear reason for that lingering guilt, much less any lasting and meaningful solution to it, unless we acknowledge the existence of a moral Lawgiver to whom we must give account for our behaviour — and who is also able to forgive and cleanse us from our sin.