The objection is strong only against a crude slogan, not against the better Islamic argument. Islam does not need to prove every detail of metaphysics beyond all possible denial; it argues that a contingent, dependent universe points more reasonably to a necessary Creator than to a brute, unexplained fact.
The strongest form of the challenge
The critic says: "You cannot simply argue that every part of the universe has a cause, therefore the universe has a cause. That is a fallacy of composition. And the Principle of Sufficient Reason - the idea that everything has an explanation - is not proven. Perhaps the universe just exists, with no explanation. Perhaps causes stretch back infinitely. And if God is necessary, maybe everything He causes becomes necessary too, which would erase contingency."
That is a serious objection. It rightly rejects lazy arguments. A Muslim should not answer it with slogans.
What the Islamic argument is really saying
The Quran's argument is not a technical syllogism about parts and wholes. It presses a deeper question: can dependent reality explain itself?
Were they created by nothing, or were they themselves the creators? Or did they create the heavens and the earth? Rather, they are not certain.
Quran 52:35-36
The point is simple and forceful. Something contingent - something that could have failed to exist, could have been different, and has no necessity in itself - does not explain its own existence. The universe, whether finite or vast beyond imagination, appears like this: changing, composite, measurable, law-governed, and not self-evidently necessary.
So the argument is not: "Every item inside the universe has a cause, so the whole universe has a cause." Rather, it is: "A totality made only of dependent realities does not become independent merely by being called a totality." If every lamp is receiving light from another lamp, an infinite row of borrowed light still has not explained why there is light at all.
Brute fact is possible to say, but costly to believe
Can someone deny the Principle of Sufficient Reason and say, "The universe is just a brute fact"? Verbally, yes. It is not like saying a square circle exists. But it comes at a price.
Reason normally asks why contingent things exist rather than not. Science itself assumes that reality is intelligible, that events are not sheer arbitrary intrusions with no account. A limited explanatory principle is enough here: contingent existence calls for explanation. Denying that principle exactly where the question becomes ultimate looks less like intellectual humility and more like stopping inquiry at the universe by preference.
Islam says the stopping point should not be a changing, composite, contingent cosmos. It should be the One whose existence is not borrowed, whose being is not assembled, and who is not one item inside the chain.
Allah is the Creator of all things, and He is, over all things, Disposer of affairs.
Quran 39:62
Infinite regress and modal collapse
An infinite regress of dependent causes does not solve dependence. Even if one allowed an infinite past for argument's sake, the question of existential dependence remains: why does this whole dependent order exist at all? Classical Muslim theologians and philosophers differed in some details, but they agreed that dependent being requires the Necessary Being.
As for modal collapse, it does not follow that if God is necessary, everything He creates is necessary. A necessary agent can have a free will. The existence of the Creator is necessary; the particular created order is not. God could have created otherwise, or not created this universe at all. His will is not forced by something outside Him, and His act does not become necessary in the way His essence is necessary.
So what does the argument establish? It establishes a powerful rational case for a necessary, independent, uncreated source of all contingent reality. By itself, it does not prove every doctrine of Islam. For that, Muslims also point to revelation, prophethood, the Quran, and the life of the Prophet (PBUH). But the theistic starting point is not defeated by calling the universe a brute fact. That is not an explanation; it is the refusal of one.