Studies and observation show religious people are not more moral, and are sometimes worse-behaved, than atheists — so religion adds nothing to morality.

Why people find it persuasive

This tracks common experience: plenty of irreligious people are kind and generous, plenty of religious people are hypocritical or cruel, and some social science (on things like church-attendance and certain measures of prejudice or in-group bias) complicates any simple 'religion makes you good' narrative.

Important distinctions

• • Moral behavior vs. moral grounding (the philosophical justification for why anything is obligatory).
• • Nominal religious affiliation vs. genuinely internalized religious conviction and practice.
• • Christianity's descriptive claim about human moral behavior vs. its actual claim about universal human sinfulness.
• • Correlational social-science findings vs. a tightly controlled causal claim about religion's moral effect.

Christian response

• • Concede the empirical claim substantially: this is not actually in tension with Christian teaching, since Christianity does not claim that believing in God makes one automatically or measurably more virtuous than unbelievers — in fact it explicitly claims the opposite starting point, that all people, religious and irreligious alike, are morally compromised (Romans 3:23), so finding religious people who behave badly is exactly what the doctrine of universal sinfulness predicts rather than something that embarrasses it.
• • Reframe the actual philosophical claim under dispute: the argument from morality is not 'theists behave better than atheists' (a sociological claim about behavior) but 'objective moral value and obligation require a transcendent ground' (a metaphysical claim about the foundation of morality) — these are entirely different claims, and refuting the first does nothing to the second.
• • Point out that much of the relevant social science is methodologically contested (measures of 'religiosity' vary widely, self-selection and confounds like socioeconomic status and community structure are hard to control for, and findings are frequently mixed rather than uniformly negative for religious populations, e.g., robust findings link religious practice to higher rates of charitable giving and volunteering in many studies), so treating any single study as settling the matter overstates the evidence.
• • Note that hypocrisy is a real problem the Christian tradition itself names and condemns sharply (Jesus reserves his harshest public criticism for religious hypocrisy, not for irreligion, in passages like Matthew 23), so pointing to religious hypocrisy is, ironically, pointing to a failure the tradition's own founder explicitly denounced rather than a counterexample to it.
• • Distinguish moral behavior from moral motivation and telos: even a Christian and an atheist performing an identical outwardly kind act may differ in what grounds the obligation and gives the act ultimate significance, which is the level at which the moral argument for God actually operates, rather than at the level of who scores higher on a given behavioral survey.

Christian counterresponse

Most careful theistic ethicists never claimed religious belief was practically necessary for moral behavior — they hold a more modest ontological claim that God is necessary for morality's ultimate ground and full rational justification, which is compatible with irreligious people living admirably moral lives by drawing (often unknowingly) on a moral order they did not have to consciously ground philosophically to benefit from or act in accordance with.