The argument is worth taking seriously as a question about alternative explanations, but the Quran's mention of jinn does not make them its authors. In the Quran, jinn are listeners, accountable creatures, and possible liars - not the source of revelation to Prophet Muhammad (PBUH).
What the objection is really claiming
The strongest form of the objection is not merely that Muhammad (PBUH) was called majnun. It is that several details seem to fit a spirit-origin theory: the Quran speaks about jinn, a group of jinn hears and responds to it, and the earliest revelations were physically demanding. Perhaps, critics argue, Muhammad (PBUH) experienced a form of possession or received communication from a powerful unseen being. Since both divine revelation and jinn influence are invisible explanations, they say Islam must do more than simply deny the accusation.
That is a coherent hypothesis to consider. It does not, however, follow from the evidence. A hypothesis must explain all the evidence, not only selected features that resemble it.
What Surah al-Jinn actually says
Say: It has been revealed to me that a group of jinn listened and said, "Indeed, we have heard a wondrous Quran. It guides to the right way, so we have believed in it, and we will never associate anyone with our Lord."
Quran 72:1-2
The jinn are presented as hearers of the Quran, not its authors. They learn from it, believe in it, and describe it as guidance. The passage is no more evidence that jinn composed the Quran than a human listener's testimony would show that he composed a speech. In fact, the jinn's words reinforce the Quran's central claim: worship God alone.
The Quran also directly rejects the idea that devils brought it:
And the devils did not bring it down. It is not suited to them, nor are they able to do so.
Quran 26:210-211
Thus the relevant question is not whether jinn exist, but whether the text's message and history are best explained by them. The Quran portrays devils as deceptive and opposed to revelation, while the believing jinn recognize the Quran as guidance from God.
What about the accusation of being majnun?
Your companion is not mad.
Quran 81:22
In the language of the Meccans, majnun could mean one whose mind was affected by a jinn. But an opponent's label is not a diagnosis, and the Quran records it as an accusation to be examined, not as evidence. Muhammad (PBUH) remained consistent in teaching, judgment, conduct, and message over many years. He did not claim private power or ask people to worship him; he repeatedly placed himself under God's command.
The physical strain of revelation also does not establish possession. Authentic reports describe revelation as demanding, including the Prophet (PBUH) sweating even on a cold day. The same reports say that he accurately retained and conveyed what was revealed. Distress can accompany a genuine encounter with the unseen; by itself, it identifies neither God nor a jinn as the source.
So this argument establishes that an alternative explanation can be imagined. It does not establish that jinn inspired the Quran, nor that Muhammad (PBUH) was possessed. The Quran's own account, its message, and the Prophet's sustained life and teaching point instead to revelation from God.