[M]any naturalists are morally decent people... but what justification could these naturalists have for maintaining the ideals and holding the values that they do maintain and hold? Where do these ideals come from if, at ontological bottom, it is all just "atoms in the void"? And why ought we live up to them? Where does the oughtness, the deontic pull, if you will, come from? If ideals are mere projections, whether individually or collectively, then they have precisely no ontological backing that we are bound to take seriously.
These are important questions - indeed, I've asked about 'deontic pull' (or 'normative force') before. But I don't see how any of these concerns are unique to naturalism.
Naturalists hold value to be reducible to natural facts (perhaps facts about human desires, and what would best fulfill them), rather than a distinct and irreducible ontological category. But why should that give them "precisely no ontological backing"? They are literally backed by their naturalistic 'reduction basis'. (Does the reduction of water to H2O make water any less real?)
BV asks why we should care about values that are merely part of the natural world. But if value is something apart from the world, why should we care any more about that? Why are non-natural values any more worthwhile than natural ones? Moreover, if we're causally isolated from values (being non-natural and all), how could we care about them? How could we even know of their existence?
Opponents of naturalism often claim that God grounds values and gives life meaning. My previous post on God-given Value disputes this, and I still haven't heard any satisfactory response. What difference does God make? What makes doing God's bidding any more meaningful than doing your own, or someone else's? Why obey divine commands at all?
I'm not sure I've understood him correctly, but BV hints that his only reason for behaving morally is a prudential fear of divine punishment:
If only naturalism were unmistakably and irrefutably true! A burden would be lifted: no God, no soul, no personal survival of death, an assured exit from the wheel of becoming, no fear of being judged for one’s actions.
Of course, just as the amoral theist behaves morally for fear of divine censure, so might an amoral atheist behave morally for fear of social censure. So the afterlife is not the only possible prudential reason to behave oneself (though it would provide the strongest one!).
More importantly, prudence is of little relevance to the broader debate. For one thing, it is distinct from ethics - I still don't see how religion gives us reasons to care about morality (as opposed to using it merely as a means to secure a pleasant afterlife). Further, it does not explain why we should care even about being prudent. If life is meaningless, what makes the afterlife any more meaningful? Surely extending worthlessness forever cannot make it worthwhile?
My questions aren't rhetorical - I'd genuinely like to hear theists' answers, if they have any. We hear a lot about how God gives your lives meaning, but how is that? What meaning or value does God provide that we would otherwise lack? I just don't see it.