One of the most common things said by people who leave religious belief is that they did not lose their morality when they left. They remained caring, honest, committed to justice, and in many cases more genuinely ethical than some of the religious people around them. The observation is often true. The observation is also beside the point.
The question is not whether irreligious people can be good. They clearly can. The question is whether irreligion can adequately explain why goodness is real, whether on a purely secular account of reality moral facts exist, and if so what sustains them.
The lived experience and the philosophical problem
Here is the gap. When an irreligious person says “torturing children for entertainment is wrong,” they are not saying “I dislike this” or “my culture disapproves of this.” They are saying something stronger: this is genuinely, objectively, morally wrong. Wrong regardless of what any individual or culture believes about it, wrong in a way that holds even if everyone on earth decided it was acceptable.
The stronger claim is moral realism. Moral realism is very difficult to ground on a purely secular account of reality.
The physical universe, as science describes it, is a system of descriptive facts, facts about what is the case. Moral facts are normative, facts about what ought to be the case. The gap between descriptive and normative facts is one of the oldest problems in philosophy. You cannot derive an “ought” from an “is” by any logical operation on purely physical descriptions. Where, then, do moral facts live in a universe that contains nothing but physical processes?
The secular alternatives
Several secular alternatives to moral realism are on offer. The most honest is moral error theory, the view that moral claims are systematically false because there are no objective moral facts. The position is coherent. Almost no one actually lives by it. The moment you treat someone unjustly and they protest, you are both appealing to a standard that you implicitly believe is real.
Another option grounds morality in human flourishing: actions are right if they promote flourishing, wrong if they diminish it. The position has genuine force. The position faces one question: why ought we to promote flourishing? The question is itself a moral question. The question cannot be answered by appealing to the facts about flourishing without already assuming that what is good for humans morally matters, which is precisely what needs grounding.
A third option is evolutionary ethics: moral beliefs are the output of natural selection, shaped because they promoted survival and reproduction in ancestral environments. The account explains why we have the moral beliefs we do. The account does not give us any reason to think those beliefs are true. Evolution selects for flexible behaviour, not moral accuracy. An evolutionary account of morality, followed honestly, leads to the conclusion that our moral beliefs are useful fictions, which is something other than what the person making confident moral claims actually believes.
The genealogy problem
Secular ethics, when traced historically, tends to reveal an unexpected dependence on the theistic frameworks it claims to have left behind. Concepts like the inherent dignity of every human being, the universal binding force of justice, the moral significance of consciousness wherever it occurs, the obligation to care for those who cannot reciprocate: each of these has its mature philosophical articulation in monotheistic intellectual traditions and was carried into secular ethics largely by inheritance.
The secular ethics that confidently asserts the dignity of every human person without distinguishing race, class, or status is using a concept worked out across centuries by thinkers who grounded it in the doctrine that every person is created by God in a position of fundamental equality before Him. The secular ethics that takes universal human rights seriously is using a concept that emerged from theological reflection on each person as bearing the image (in Christian formulations) or carrying the trust as khalīfah (vicegerent, in Islamic formulations). Strip out the theological grounding, and the concept floats free of the framework that gave it weight. Some philosophers have noticed this and worked to reground these concepts on secular foundations. The reconstructions tend to be either circular (assuming what they need to prove) or dilute the strong intuitions to the point where they no longer match what most people actually believe.
What theism offers
Theism offers a grounding for moral realism that secular accounts lack. On the theistic account, moral facts are not invented by human beings or selected by evolution. They are grounded in the nature of God, not in arbitrary divine commands but in the objective standard of goodness that a being of unlimited goodness constitutes. Moral facts are necessary truths about value, analogous to mathematical truths, grounded in a reality that does not change with human cultural fashion.
The Islamic articulation of the source of objective moral facts is direct:
The verse establishes a moral architecture: God commands what corresponds to His nature (justice, excellence, generosity) and forbids what violates it. The commands disclose the moral order built into the structure of reality by the Being whose nature constitutes that order. The grounding question (what makes these moral facts facts?) finds its answer in the One whose existence is necessary and whose nature includes the standard of goodness as a non-arbitrary feature.
The fitrah and the moral compass
Islamic theology adds a complementary claim. The capacity to recognise the moral order is built into every human being:
The verse identifies the moral and spiritual orientation of the human creature as given by God in creation. The capacity to recognise right from wrong is innate to being human. This is why irreligious people who have left explicit theistic belief continue to recognise basic moral truths: the recognition is not learned through religion. The recognition is recovered through the operation of the conscience God installed.
The hadith literature reinforces the point at the level of practical experience:
The Prophet ﷺ instructs the listener to consult their inner sense as a moral compass. The instruction presupposes that the inner sense is reliable, that conscience tracks something real, and that the response of the heart to right and wrong is itself evidence of the moral order. The instruction is given to a Muslim, but it presupposes a capacity that is universal. Every human being, religious or not, can perform the consultation the Prophet describes. The reliability of the result is what the irreligious moral life depends on without acknowledging.
Where the argument lands
The fact that only theists can be good is not the claim being made. The claim is that the moral experience irreligious people rely on (the felt reality of genuine right and wrong) is better explained by theism than by any secular alternative. The person who left religion but kept their morality has kept more of the theistic framework than they realise.
The issue becomes clearer once Islam is approached as a coherent moral and intellectual vision rather than a pile of disconnected rulings. Questions of belief, revelation, ethics, and human dignity illuminate one another, and many objections weaken when that wider picture is kept in view. The irreligious life that holds firmly to the dignity of persons, the binding force of justice, and the moral significance of conscience is using the architecture of a tradition it has officially left. The architecture remains sound. The question is whether the foundation that built it can be removed without the building eventually settling.