For instance, M says this:
The New Testament adds much to our understanding of heaven (and hell), but we are still not permitted to add our own subjective ideas and experience-based conclusions to what God has specifically revealed through His inerrant Word. Indeed, we are forbidden in all spiritual matters to go beyond what is written (1 Corinthians 4:6).
What does it mean to "go beyond what is written"? What does it mean to be "not permitted to add our own subjective ideas and experience-based conclusions to what God has specifically revealed?" It's not perfectly clear what exactly M means by those words, but what is clear from the context is that M thinks there is something wrong with the NDE books in principle. You just shouldn't claim to know extra-Biblical stuff like these people are claiming.
But what is wrong with the following: I believe (and believe I have excellent reason to believe) that God has performed miracles in my life and others that I know. But, let's be honest, I'm not exactly in the Bible!! Nor is there anything in the Bible that guarantees that such and such miracle today was caused by God. There is some scriptural evidence (e.g. there's reason to believe from Scripture that God is in the business of healing), but I can't simply look in the Bible to see if God healed this person I know. Yet there's nothing wrong with believing that God did such a thing. So why think that if I wrote a book about my life and included miracles by God that I'm somehow violating a Scriptural mandate? I see no good reason to think this way. But then why think reporting something about heaven is off limits? If God heals my son, then it's true that God in heaven healed my son. If I know God healed my son, then I know something true about heaven, namely, that God in heaven healed my son.
Let us also note that none of these books are thought to BE SCRIPTURE (which would be heretical) or to contain propositions which the authors advocate should BECOME CHRISTIAN DOCTRINE. There's no adding to doctrine or scripture being advocated in these books. The authors are reporting additional things they (purportedly) take to be true about heaven (which, nonetheless, we might have good reason to be skeptical about). Perhaps some of these authors have illicit reasons for saying what they do (e.g., perhaps some are in it for the money), but perhaps some genuinely believe their experiences were veridical and think that these stories will help bolster the faith of others. I get the impression that P&M think the only legitimate mode of theologizing is to open up a Bible (King James only?) and simply read it out loud.
Another reason P&M think there is something wrong with these books is because they think there's good evidence that no one has been to heaven except for Jesus. For instance, M cites the following (P adds Proverbs 30:4 which is similar):
John 3:13 says, “
No one has ascended into heaven except he who descended from heaven, the Son of Man.” And John 1:18 says, “
No one has seen God at any time.”
I don't know exactly what to make of John 3:13, but Jesus can't be saying that he's already ascended into heaven, which a straightforward reading of the verse suggests. So our interpretation can't be that straightforward. Still, suppose this passage rules out all bodily ascensions (adding curiosity about where the bodies of Elijah and Enoch went). That's still not inconsistent with someone's soul being in heaven until the resurrection of the body (e.g., the one thief on the cross). So if ascension can mean bodily ascension, then John 3 and 1 aren't obviously inconsistent with some assertions in these popular books. But even if the souls of people aren't in heaven, it's still an open question whether they had visions of being in heaven without being materially or immaterially present. I don't know what would rule that out in principle.
Much more needs to be said, but the matter is complicated. It's more complicated than P&M let on.