The central claim some theists make is that objective morality requires God as its foundation. But this immediately raises a question: on what basis is that claim itself grounded? If a person says, “God grounds objective morality, and I ground this assertion on myself,” then the foundation of the argument is not God but the individual's own judgement. That means the believer is ultimately relying on personal moral intuition to assert God's role—exactly what they deny atheists can do.
Atheists, therefore, do not need to start by asking whether God exists. A more productive focus is the independent nature of moral reasoning. If moral judgements arise from human capacities such as empathy, reasoning, and shared interests, then morality does not depend on divine commands.
Appealing to God does not solve the issue of moral grounding. It only shifts the question back a step: How does the believer know God is good, or that God’s commands are morally binding? If the answer depends on human evaluation—“I judge God to be good”—then morality is already grounded in human judgement, not in God. And if one instead claims that whatever God commands is right simply because God commands it, then morality becomes arbitrary. If one claims that it is not God's commands so much as what his nature commands that is no better.
To fail to admit the issue and shift like that makes it all worse. Whatever it results in, it is not morality.
We can therefore discuss morality without invoking divine authority. People can act ethically because actions have real consequences for the wellbeing of others and for society. Responsibility and meaning arise from our relationships, our choices, and the impacts we have—not from supernatural oversight.
In short: if the claim “God grounds morality” ultimately relies on human judgement, then human judgement is the real foundation. Atheists need only show that we already rely on human moral reasoning, with or without God, and that ethical behaviour does not require divine endorsement.