As much as the NIV debs about the evidence of the manuscripts (the NIV's preface has a section on the manuscripts that they use, including the MT, and the N-A eclectic text), it is also a debate about worldview. Simply put, if you believe that the King James version is the only authentic version of the Scriptures, no argument for the NIV will sound convincing because it goes against the presupposition of believing KJVOnlyism.
On the other hand, if you approach the NIV with the perspective that there are a number of faithful renditions of the Scriptures into English, you can approach the study of the NIV in a non-binary way. Non-binary meaning that the possibilities of the NIV are more than just either it being the accurate Scripture version, or a Satanic perversion. The NIV is more like a literal/paraphrase rendition of the Scriptures, that gets the point across while still being easy to read. I think you can settle down on this translation by saying it is "a" translation of the Scriptures into English, but not as wooden as the ESV or NRSV, and not as much of a paraphrase as the NLT or the Message.
If you believe there can only be one definite translation of the Scriptures into English, you're going to reject all other translations than the one you prefer from the outside, and never consider that there can be more than one accurate translation into English so that mindset will reject the NIV. But if you believe that there can be more than one accurate translation of the Scriptures into English, you won't have a problem with accepting the NIV as an actual decent translation.
