Simple question: What are the best arguments for the divine inspiration of the longer ending of Mark (Mark 16:9-20), according to believers in its inspiration?
These are examples of articles presenting arguments against Mark 16:9-20's inspiration:
Answers rebutting these articles will be highly appreciated.
A related question illustrating why the question about inspiration is important: Are the signs mentioned in Mark 16:17-18 universally expected of all true believers?
The following is quoted from this article at the Early Church History website which outlines the very early attestation of the longer ending of Mark:
Irenaeus, Justin, Tatian and Hippolytus were very early Christian men (100’s) who were born and raised when some who had heard/seen Jesus as youngsters or teens and some of the Seventy Disciples were still alive. It is very persuasive that all four of them, born in the 100’s AD, KNEW AND CITED the Long Ending of Mark, the ending that has been traditionally in the New Testament. The book by Irenaeus quoting Mark 16:19 is OLDER than the earliest manuscripts we have of the Gospel of Mark. These four attestations of the Long Ending being included in Mark pre-date any edition of any other early Bibles.
Here is an exerpt from another article arguing that, even if the longer ending is acknowledged as a later addition this in no way disqualifies it from being considered as inspired scripture:
As, then, the facts of the case, and the early reception and transmission of this section, uphold its authenticity, and as it has been placed from the second century, at least, at the close of our second canonical Gospel;—and as, likewise, its transmission has been accompanied by a continuous testimony that it was not a part of the book as originally written by St. Mark;—and as both these points are confirmed by internal considerations—
The following corollaries flow from the propositions already established:—
I. That the book of Mark himself extends no farther than ἐφοβοῦντο γάρ, xvi. 8.
II. That the remaining twelve verses, by whomsoever written, have a full claim to be received as an authentic part of the second Gospel, and that the full reception of early testimony on this question does not in the least involve their rejection as not being a part of Canonical Scripture.
A. It was quoted by early Church fathers.
The versus in question were quoted by Irenaeus, Justin, Tatian and Hippolytus in the second century AD [1]. While manuscripts from these authors don't predate 4th century Sinaiticus manuscripts, it seems unlikely that their writings were all later augmented to include this commentary. Thus, we can conclude that Mark 16:9-20 at least dates back to very early Christianity, older than any extant manuscripts.
B. Divine inspiration does not necessarily depend on Mark's original authorship.
Did Moses write Genesis, or if not who did? Does that answer actually affect Genesis's canonical status? Whatever belief you have in Mark as a writer of authentic gospel truth, you might extend that belief to the author of these 12 verses.
C. Criticisms of doctrinal uniqueness are overstated.
That first article questions four doctrines:
(1) Baptismal Regeneration
He that believeth and is baptized shall be saved; but he that believeth not shall be damned.
Mark 16:16
Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God.
John 3:4-5
(This will depend largely on your view of baptismal regeneration, and the interpretation of John 3.)
(2) Snake Handling
(3) Drinking of Poison
They shall take up serpents; and if they drink any deadly thing, it shall not hurt them
Mark 16:18
Behold, I give unto you power to tread on serpents and scorpions, and over all the power of the enemy: and nothing shall by any means hurt you.
Luke 10:19
(4) Healing by Laying Hands on the Sick
they shall lay hands on the sick, and they shall recover.
Mark 16:18
all they that had any sick with divers diseases brought them unto him; and he laid his hands on every one of them, and healed them.
Luke 4:40
[1] https://earlychurchhistory.org/beliefs-2/long-or-short-ending-in-mark/
Space is left at the end of Mark in the Codex Vaticanus as if the copyist knew of the longer ending. 
The missing column is the only column in the manuscript missing in the NT.
Another feature of the manuscript is distigmai or umlauts (a series of horizontal dots) in the margin. Philip Payne (Philip B. Payne and Paul Canart, The Text-Critical Function of the Umlauts in the Vaticanus With Special Attention to 1 Corinthians 14:34-35) gave the meaning of the distigmai in 1999 as a mark to indicate the scribe knew of variant readings for the line so marked. The ending of Mark is marked with distigmai.
Dr. George Salmon (Introduction to the New Testament, John Murray, London, 1891, p. 146) says the endings in the Vaticanus and Sinaiticus of Mark 16 have been altered and emendations added by the same scribe. Since the text of the Vaticanus differs significantly from the Received Text (Swete, Henry Barclay, An Introduction to the Old Testament in Greek, Cambridge, 1902) was edited in the 10th or 11th century (Bruce Metzger, Manuscripts of the Greek Bible: An introduction to Greek Paleography, New York, Oxford, Oxford University Press, 1991, p74), and was written by two or three different hands (Constantin von Tischendorf, Edito ocatava critica, ed. C.R. Gregory Lipsiae 1884, p360), and since we have so many earlier attestations to the longer ending as noted in the answer here by Mike Borden, it is worth asking if the text was altered.
I respectfully dissent from the view that the textual variant at the end of Mark's Gospel is simple--it is a challenging question.
Kelhoffer's book on the subject is more than 500 pages. My own published work on the subject is on YouTube here.
In this post, I will argue that the statements in the last 12 verses of Mark are true, not necessarily original. If these verses are true, the following argument can be applied:
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In another post I reviewed 6 arguments for the inspiration of the Bible--I will apply those arguments to the last 12 verses of Mark (aka Mark 16:9-20 aka the "L12VOM"). Those taking issue with premises 1, 2, or 5 above should consult this prior post.
1. Archeology - to my knowledge, there is no archeological evidence that is specific to the last 12 verses of Mark; however, there is ample archeological evidence for the historical accuracy of Luke-Acts (one example of many here); to the extent that the L12VOM parallel the Lukan narrative, they are not only corroborated by an early source, but by an early source that itself is well corroborated.
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2. Eyewitness authorship - there is no significant effort in any scholarly circles to argue that the Gospel of Mark was written by an eyewitness. Those who disregard the value of anything published before 1750 generally claim that the author is unknown. Those who consider Papias & Clement of Alexandria to be reliable, well-informed sources generally acknowledge that the author was John Mark, who served in missionary labors with Peter (and Paul).
There is precious little evidence that Mark was an eyewitness of much/any of the material in his Gospel. Rather, the early historians indicate that it is Peter's testimony that was preserved by Mark (see esp. Eusebius quoting Papias in HE 3.39).
The eyewitness argument probably won't help us much with the L12VOM (as an interesting side-note, there is one ancient Armenian manuscript which appears to attribute these verses to Aristion. Papias indicated that there was an early, influential eyewitness of Jesus named Aristion. Interesting possibility).
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3. Prophecy
The Book of Acts affirms most of the prophecies found in verses 17 & 18. The global presence of Christianity in the world today supports the claim that the commission in verse 15 is succeeding.
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4. The Historical Argument for the Resurrection
This argument works best for the L12VOM if we acknowledge that the Gospel of Mark was written during the lifetime of key eyewitnesses of the resurrection.
If the resurrection of Jesus is considered a true, historical event (I very much believe it is), and the Gospel of Mark was written within a few decades of Easter (my work-in-process video series showing this can be found here), misquoting Mary Magdalene & the 11 apostles at a time when they were around to correct misstatements is unlikely to be successful. However, if the L12VOM are a later addition to the Gospel of Mark, even if the rest of the book was written within a few decades of Easter, it doesn't mean the L12VOM were.
This is argument is very potent for supporting some of the most important claims in the Gospels, but is not particularly helpful for the L12VOM.
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5. Private inspiration
If God speaks through the Holy Spirit and manifests the truth of what someone has read, this is an epistemologically significant endorsement. I must admit that I do not know many people who report that they have asked God and received an answer specifically as it relates to these verses from Mark.
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6. Public revelation
If God speaks through an authorized representative and indicates that a text is inspired, the claim is solid as long as the spokesperson is reliable.
The presence of nearly everything in the L12VOM in Matthew, Luke, John, and Acts is a good indicator that, at the very least, the events related are true.
As noted in other posts, Irenaeus of Lyons (writing circa 180) not only quotes from the L12VOM, as several other early writers do, but he specifically tells us this material is from Mark! Irenaeus provides a very strong affirmation that these words were accepted as authoritative by 3rd-generation Christianity. This may not count as public revelation, but it is a significant public endorsement.
But what of the specific words attributed to Jesus in verses 15-18??
Those of my faith have a direct answer to this one. The Book of Mormon endorses these words without ambiguity: see Mormon 9:22-24.
(Nerd alert--incidentally, the following verse in Mormon chapter 9 says I confirm all my words, even unto the ends of the earth. I find it quite interesting that the prior verses do just that in defending the truth of one of the most debated passages of the Bible. In fact, between the Book of Mormon and the Joseph Smith Translation, 5 of the most petulant Biblical attacks from the discipline of textual criticism are rebutted. Modern revelation supports the last 12 verses of Mark, the reality of the Sermon on the Mount, Jesus' agony in Gethsemane, His statement of forgiveness on the cross, and that the story of the woman taken in adultery really happened. 5 significant Biblical passages the skeptics would love to throw out are confirmed as real--regardless of who wrote them--by modern revelation)
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Conclusion
Even if we do not know who wrote them, there is good reason to believe the last 12 verses of Mark are true. According to the deductive argument at the beginning of this post, it is, therefore, reasonable to conclude that these verses are inspired.
Appendix--engaging with other arguments
Yes!
The heavyweight Alexandrian texts used to extricate the L12VOM from many modern Bibles were written in the 4th century. That's very, very early, as major Biblical manuscripts go. But Irenaeus was reading from one or more copies of the Gospel of Mark written ~2 centuries earlier. (even arguing for the early-nature of the material in Codex Vaticanus by comparing it with P75 doesn't overcome this argument--Irenaeus almost certainly had access to information earlier than the common ancestor of P75 & Codex Vaticanus)
What does it mean, though, that Irenaeus considered material from the L12VOM to be authoritative? I readily acknowledge that does not guarantee that Mark wrote it. It could mean:
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I don't think there is sufficient grounds to hold confidently to this conclusion. My video addresses this in detail, but the narrative break, the narrative style, and the vocabulary all hint at a different mind at work. Furthermore, what Codices Sinaiticus & Vaticanus do show, is that as early as the 4th century there were Christian scholars who doubted the originality of these verses. I discuss in the video (and a little bit above) why inspiration & lack-of-originality are not mutually exclusive properties.
I am of the view that the most likely explanation is that the original ending of the Gospel of Mark was lost around the time Mark left Rome for Alexandria (~AD 55), and Roman Christians rewrote it from memory before Mark returned to Rome (~AD 62). Mark found their rewrite acceptable and didn't challenge it--it got the message right even if it wasn't in his own words.
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If the oldest (earliest) manuscripts don’t have the longer ending, it points to a later addition by some scribe who might have considered the Mark 16:8 a strange way to end John Mark’s work - could be, but:
We must not lose confidence in the validity and authenticity of God’s inerrant Word - this is a question of theology; we need not equate the terms "inspired" and "inerrant" in order to make an argument about these verses.
For instance, Clement of Alexandria and Origen both show no evidence in their writing that they embraced a longer ending of Mark. Everything in their writing points to the ending of Mark at 16:8 - that's quite a stretch.
Eusebius, the church historian born approximately AD 260, claims that the most accurate copies and “almost all copies” of Mark’s Gospel ended at Mark 16:8 - the authorship of this particular "Eusebian" text is disputed. We don't know that Eusebius wrote it. At the very least, though, somebody around this time wrote it, and acknowledged there were already doubts about these verses.
Jerome likewise points out that Mark 16:9-20 was absent from the majority of the manuscripts available during his lifetime. - yet Jerome determined it was appropriate to include these verses in his Vulgate translation.
When reading the Ante-Nicene Fathers (the ancient writings leading up to A.D. 325), it’s apparent that they viewed the ending of the Gospel of Mark to be 16:8 rather than 16:20 - it is not so apparent. Some quote the L12VOM (a), some do not (b). Some believed these verses were accurate (c), some did not (d). But we cannot say with certainty that an author in group "b" is necessarily also in group "d".
Buice suggests several doctrinal topics in the L12VOM are problematic--I disagree.
Baptismal Regeneration - taught at least as clearly in John 3 as it is in Mark 16
Snake Handling - he doesn't say people should try it out. It's a promise of protection, not an invitation to perform circus stunts (and Paul was protected from a venomous snake on Malta).
Drinking of Poison - same as the snake handling (and there is an early Christian tradition that Justus was given something poisonous to drink and survived)
Healing by Laying Hands on the Sick - also found in James 5, and similar accounts are found in many places in both OT & NT.
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the oldest manuscripts are known to be the most accurate because there were fewer generations of copies from the original autographs - this vastly oversimplifies textual criticism. With only a little bit of prestidigitation, the same argument could be made that the KJV is therefore a more reliable English translation than modern translations that use the Critical Text, because the KJV is older (and the KJV includes the L12VOM =) )
In reality, ending his Gospel in verse 8 with the description of the amazement of the women at the tomb is entirely consistent with the rest of the narrative - my aforementioned video extensively rebuts this claim.
