You said: Here's a thought; the Qur'an is not God's words - they are Muhammad's.
If
we were to say that none has seen God and he doesn't exist, they give
us an argument that his likeness is that that of Air which we fail to
see by our eyes but still could feel it. For some, this argument holds
good and for some something else and for the rest nothing holds good.
Man has his own preferences, many are used to God and some aren't.
Similar is one's view about Quran
being God's word or the contrary. All of this is just a matter of your
personal sentiments and the way you would prefer to see your own share
of truth. In these cases, an admonishing tone works better than a
judgmental attitude. Neither can you disprove his point nor can he
prove his view, all you get is aversion.
Regards,
Pondering Mind.