when I debate a Muslim concerning the Quran, it always boils down to this: whomever I'm debating declares that *they* know the true meaning of the words in the book. That claim makes it a debate without meaning.
True, when literal.
False, when allegorical.
That's the thing with religious texts, if something is literally true then it should be taken literally, if something is false when taken literally, then it is a metaphor, allegory, analogy or some other kind of rhetorical trope.
Language is so flexible that you can have the same ayats and some people say it shows something scientifically false and others say it is a 'scientific miracle' (i.e 7:54, 21:31, etc).
For a Muslim there are no mistakes in the Quran because the Quran is eternal and perfect, which precludes the possibility of any errors. For a Muslim, a literally untrue verse must be a metaphor because the Quran is inerrant, a rational analysis (from the Muslim perspective) would have a huge weight of evidence to support this.
For most non-Muslims debating the issue, they probably want to show the Quran is false, so are more inclined to take things literally.
People are operating with different hermeneutical frameworks, and they are both 'right' in their own sort of ways.
So it is true that, for a believer, there are no mistakes in the Quran. Vague, poetic language is hard to pin an exact meaning on giving a wide enough potential range of interpretation to make this so. It isn't written as a scientific textbook.
The same is probably true of the Bible though, if you start from the perspective that it is true, anything can be explained away with a little creativity. Agreement ca't be reached though as each side is looking at a completely different set of 'evidence'.