Upvote:2
No, absolutely not at all
It is well-known that the Bible was not written down as a single chunk, intended from the start to be taken as infallible. The process by which those writings were declared to be Scripture took hundreds of years, and the addition of the last twelve verses of Mark certainly predate that. So at the point where the canon of scripture was defined, those twelve verses were in Mark.
Upvote:9
Short answer, no. Not at all.
It would count as plausible deniability to the straw-man definition of "the inspired and infallible word of God", but only to the false straw-man understanding.
The problem is that, almost no denomination believes that inspiration and infallibility are attributed to modern versions/translations of Scripture. Inspiration and infallibility are attributed only to the original manuscripts, as recorded by the original authors. We have always allowed for the possibility of copyist errors, mistakes, etc. This is explained in great detail here: From a Fundamentalist standpoint, what does the phrase "Inspired, infallible, inerrant Word of God" mean?
(That is from a Fundamentalist perspective, but most denominations and traditions agree that infallibility and inerrancy are only attributed to the original manuscripts.)
This does leave the question of "If the current versions could contain mistakes, how do we know that we can depend on them? How do we know they haven't changed over time so much that they can no longer be trusted?" That's also an answered question: What is "Manuscript Evidence" and how is it useful?