Readers of Viewpoint are doubtless well-aware that I think the question of how we ground our moral beliefs is of paramount importance.
They're doubtless aware, too, that we live in an era in which some secular folk are extremely judgmental of the behavior of others, to the extent that they're willing to destroy the careers of those who deviate from what the censorious deem morally acceptable opinions or behavior.
One of the ironies of this is that the most judgmental people in our society are often secularists or non-theists yet these are the very folks who should be the most non-judgmental of all.
I say this not because I think that non-theists (or naturalists) are more noble than others but because a naturalistic worldview, which naturalists presumably embrace, offers them no basis for making any judgment at all about the moral rightness or wrongness of other people's behavior.
Here's why:
Humanity, generally speaking, shares a basic moral understanding (i.e. that loyalty is good, betrayal is bad; kindness is good, cruelty is bad; honesty is good, dishonesty is bad, etc.). This understanding seems to be inherent in human beings as though it were somehow inscribed on our DNA.
Granting that this is so, how do we explain the existence of this basic moral understanding?
There are, it seems, two possibilities. Either we've acquired this understanding through an impersonal, unguided, naturalistic process like Darwinian evolution, or we've acquired it through the intentional act of a creator (i.e. God).
There's no plausible third option. It seems that naturalism and theism exhaust all the possibilities.
Suppose then, that the answer is that we've evolved this moral understanding naturalistically. If so, then what makes acting against this understanding "wrong"? How can blind, purposeless, impersonal processes like gene mutation, the accidents of genetic drift, and natural selection impose an obligation on us today to live according to a moral understanding that evolved to suit us for life in the stone age?
Moreover, if evolution is the source of our moral sentiments then it's also the source of our propensity for selfishness, violence, and tribal hatreds. That being so, if a propensity for kindness and a propensity for cruelty have both evolved in human beings, why should we assume that it's right to be kind and wrong to be cruel?
If we insist on making that assumption then we must be comparing kindness and cruelty to some higher standard that transcends our evolutionary history, but naturalism admits of no such higher standard.
On the other hand, if that moral understanding - call it conscience - is instilled in us by a perfectly good, all-knowing creator of the universe who both loves us and has the authority to insist that we act in accord with that moral understanding, and if that creator also possesses the power to hold us accountable for how we live, then we have a good reason for thinking that we have an objective duty to live according to what our conscience tells us is good and right.
On naturalism we can certainly intuit that we should be kind rather than cruel, selfless rather than selfish, but we have no obligation to follow those intuitions. Human nature being what it is we're often pulled and tugged in a direction opposite to what we think we should go, and in a naturalistic universe there's no compelling reason why we should resist those tugs. It's not morally wrong to yield to them.
In sum, if naturalism is true then ethics is just a bunch of socially fashionable and arbitrary conventions which have no real moral binding force.
If theism is true, though, there can be genuine moral right and wrong and genuinely objective moral obligations.
Anyone who believes that we have a moral obligation to do justice and to show compassion to the poor and oppressed should, if they're consistent, be a theist.
If they're a non-theist and nevertheless maintain that there are objective moral obligations they're irrationally importing those beliefs from an alien worldview (theism). Their own worldview offers no basis for them.
It's one of the more remarkable features of our times that so many secular people who pride themselves on their intellectual perspicacity either don't see this or don't mind living with the incoherence.