The idea that someone’s morality comes from a god is like the idea that their cellular structure is assembled by a god. Biochemistry describes a different process in which macromolecules from food are broken down and/or sorted into the structures in a process of self-assembly. This occurs over developmental and evolutionary time and the idea of assembly from extrinsic sources is not plausible.
My comparison suggests that a science of morality might yield or has already yielded similar conclusions, viz. that morality develops over developmental and evolutionary timescales by a process of self-assembly. Key theoretical pointers are theory of mind and game theoretic notions for the two timescales, respectively. There is much to elaborate on here, but this is not the purpose of this post. Suffice it say that anticipating this general outcome of research is not unreasonable. It fits the pattern of scientific discovery in general, replacing implausible but intuitively appealing skyhooks with a multitude of cranes to do the heavy lifting of explanation (to borrow Dennett’s admittedly tendentious phrasing).
For those who disagree with me, there are several versions of what it means to say there is no morality without a god. First this might mean that if you do not believe in a god (or in this role for such an entity) then you cannot be a moral person (implying that atheists are necessarily nasty). Second it might mean only that a god plays this role regardless of whether you are aware of that fact (so atheists and theists are equivalent). But there is a third and intermediate position which posits that your being aware of a god’s role in planting morality’s seed in you in will enhance your access to it in some way. The details of this are not important, but the fact that there are several ways this can be imagined (e.g., that you accept a universal love invisible to others, that you can hear a god’s advice, etc.) makes it intuitively more appealing and plausible, at least to deists or theists. (For completeness, the supernatural realm is not always so appealing and it is plausible to be angry or frightened by powerful agents, like witches, and wish to be an unbeliever).
But for those who agree with me, there are also several versions of what it means to say that religion is not a source of morality. First it might mean that religion is essential for the development of morality but is not its source (so that to be good you must be culturally Christian, if not a theist, for example). Second it might mean that religion has nothing to do with morality (so theists and atheists are equivalent). But again there is an intermediate position: perhaps religion has an impact on the development of morality over developmental and evolutionary timescales though it is not essential. (For completeness, you might posit that religion has only negative effects on the development of morality too – more below).
I find the third non-theist position plausible and to explain why I return to the analogy of biochemistry and eating. While it is true that self-assembly, not outside-directed assembly, is responsible for cellular structures, chemicals we ingest do affect physiology. The most obvious class of things ingested which can do this is drugs though all aspects of diet are relevant over developmental and evolutionary timescales. What might this mean in the context of morality?
Religions generate plausible intuitions about morality the most obvious flowing from the concept of an all-access agent (of which the Christian god is an example): crudely, if He knows everything that everyone is thinking (not just doing), then He will know what is right and what is wrong (much of this follows from Pascal Boyer’s thesis in “Religion Explained”). Moral problems are problems of social coordination and are often caused by having only partial information about another’s motives. Now this concept might be too recent in history to have impacted the evolution of morality, but it can surely affect the development of morality in individuals at least as an intuitive framework for moral expression (and possible negative connotations if access to such an agent is claimed as a special privilege). Arguably the causation here is mostly in the other direction with the plausibility of the intuition driving hazy notions about the nature of the agent (e.g., God seems to be aware of all relevant strategic information such as that spoken of in confession, but people don’t make much of His knowing any particular detail of the physical universe unless it is relevant – it isn’t often subject to debate despite the implications for how this feat of memory might be achieved (none of which is to imply it could not)).
On whether believing in all-access agents has good or bad consequences, I suspend judgement. It may be that believing in one intensifies feelings of conscience, which seems like a good thing or it may be that it promotes a command-and-control morality possibly inappropriate after childhood when most fellow humans are on an equal footing as regards privileged information (but seemingly reinforced by fictive kin notions like “God the Father”). Hence the possibility that religion is less like opium, more like an amphetamine: a moral stimulant.
All-access agents aside, religion has been around for a while so there might be a story a bit like lactase persistence waiting in the scientific wings (again with neoteny being a feature). Perhaps notions of other worlds or of reincarnation or life after death have effects on intuitions that are now tolerated or even required by our moral intuitions. I am not sure, but if there are necessary components of religion it seems plausible they may already be dispersed outside of any particular religion in the form of intuitively appealing notions and moral fables and parables.
The take home point is that nobody should prejudge the matter. Religious people do give blood more (a measure which gets round the confounding fact that charities are often religious) and religions are effective at organising the distribution of club goods from social welfare to suicide terrorism. Religion has an impact and it is likely to be complex. Understanding this is important especially if as a social democrat you are interested in the forces responsible for social solidarity and want to move beyond the religious right’s “family values” (think Mafioso – amusing comparison made by Stephen Fry) and the atheist left’s tendency to throw the baby out with the authoritarian bathwater (see this article or this talk for a slightly hyperbolic version of this sentiment).