If you had been born in Saudi Arabia you'd be a Muslim, if you'd been born in India you'd probably be Hindu — your Christianity is just an accident of geography, not truth.

Why people find it persuasive

The correlation between geography/upbringing and religious belief is extremely strong and well documented, and it's uncomfortable to notice how much of what feels like a personal, reasoned conviction actually tracks where and to whom one happened to be born.

Important distinctions

• • A causal explanation of how a belief was acquired vs. an evaluation of whether that belief is true.
• • The sociology of religious belief-formation vs. the epistemology of religious belief-justification.
• • This specific argument applied to religion vs. its equally valid application to virtually every other deeply held belief (political, moral, philosophical).
• • Initial belief-formation via upbringing vs. subsequent examination, exposure to alternatives, and reasoned adult affirmation or rejection.

Christian response

• • Name the argument precisely: this is the 'genetic fallacy' applied to religion — pointing out the causal, sociological origin of a belief (upbringing and geography) is not the same as showing the belief is false, since even a true belief has to be acquired somehow, and everyone's beliefs of every kind have some causal origin in their upbringing, environment, and available information.
• • Apply the argument's own logic universally to show it proves too much: if being born in Saudi Arabia would likely make someone Muslim, being born in a secular Scandinavian country would likely make someone an atheist, being born to Marxist parents in mid-century China would likely make someone a committed Marxist, and being born into virtually any society shapes one's views on ethics, politics, and much else — if geographic correlation with belief formation discredits religious belief specifically, it discredits atheism, political conviction, and moral conviction just as thoroughly by the identical logic, which suggests the argument proves too much to be usable selectively against religion alone.
• • Point out that this is ultimately an argument about the reliability of belief-forming processes in general, and the correct response to noticing that upbringing heavily shapes initial belief is not blanket skepticism about all such beliefs but critical examination — actually looking at the arguments and evidence for and against the specific belief in question as an adult, which is precisely what apologetics as a discipline, and honest examination of counter-evidence, are meant to enable, rather than resting content with the belief one was raised in purely because one was raised in it.
• • Note that many committed Christians (a very large number of contributors to Christian philosophy and apologetics, in fact) were not raised Christian and converted as adults after specifically examining and rejecting their prior worldview (C.S. Lewis being a famous case, moving from atheism to theism to Christianity through extended argument), and many people raised Christian have left the faith after examination — showing that geographic/familial starting point, while a strong statistical predictor, does not function as an unbreakable causal determinant that overrides evidence and reasoning for everyone.
• • Redirect to the substantive question the objection tries to bypass: whichever way someone came to hold their current religious or irreligious view, the question of whether Christianity's specific truth claims (the resurrection, the nature of God) are true or false has to be settled by evidence and argument, and no fact about how the belief was first acquired can substitute for actually doing that evaluative work.

Christian counterresponse

This is a fair and important epistemic virtue to cultivate, and it argues for humility, genuine engagement with counter-evidence, and intellectual honesty in examining one's own beliefs — which many serious religious thinkers (and this project's own approach of steelmanning objections) explicitly try to practice — but it is a call to examine belief carefully rather than a reason to conclude the belief is false, since the same humility-based reasoning would counsel equal caution about confidently held secular convictions formed the same way.