Religious belief tracks geography, not truth.
The objection, in full
Had you been born in Riyadh, you'd defend Islam with the same conviction you now defend Christianity. Lhasa, Buddhism. Ancient Athens, the Olympians. The overwhelming predictor of someone's "saving faith" is the latitude and longitude of their crib. A truth this important shouldn't depend on a postal code.
If we have a knock-down argument that the others can't have, it's strange that almost no one finds it except by accident of birth.
or, in plain terms —If I'd been born in Pakistan, I'd be a Muslim. So how is my faith "true"?
Probable arguments converge on certainty.
Belief is not arrived at by a single decisive proof, like a geometric demonstration. It is reached by the convergence of many independent probabilities — the testimony of conscience, the historical evidence for Christ, the witness of the saints, the experience of grace, the coherence of doctrine with what one already knows of the world. What I call the illative sense is the mind's capacity to weigh these together.
The accident-of-birth objection treats faith as if it were a coin flip — heads Christianity, tails Islam, decided by latitude. But a serious adult convert does not flip a coin. He weighs evidence, much of which his birth culture did not give him, and some of which it actively obscured.
That a child believes what he is told is not scandalous. It is how children learn anything at all. The question is what the adult does with the inheritance — examine it, or merely repeat it. Christianity, more than any rival, invites the examination.