RE: I suppose that is a rhetorical question?
Not strictly. If we accept the Markian passage as inspired, the question then becomes how do we UNDERSTAND the phrase, “These signs shall accompany those who believe” seeing that we don’t see these signs Jesus enumerated accompanying those who believe today.
Skeptics will say that unless we see these signs accompanying ANYONE who say they believe, then their profession of belief contradicts what Jesus said.
(NOTE: I am not agreeing with this, just presenting what I have heard from some people ).
Regarding this passage that certain theorists disclaim, largely it is because of shortsightedness in declaring some language to be plain-literal rather than figurative-literal. I have no problem with a figurative-literal interpretation of verses 17 and 18, but it may take a little knowledge of the hermeneutics--science of interpretation--to appreciate the difference. What confuses one is that there are Biblical instances where the passage is about a literal incident, such as Paul being bitten by an asp, as well as the many cases throughout the OT and the NT where the Holy Spirit has come upon a person or upon a group, with external visible manifestation of uttering languages a person was not previously familiar with, and/or magnifying The God (prophesying); the occasion given as the sign of an authentic operation of the Spirit to be noted and studied for doctrine. The Jews must have a sign, but the Greek verification demands a logical clear explanation (examples: Acts 19:6,11+;1 Cor. 1:22). This is well-covered in the doctrinal epistle to the dispersed Jews:
Hebrews 2:3-4 AV (compare Mk. 16:20):
3 "How shall we escape, if we neglect so great salvation; which at the first began to be spoken
by the Lord, and was confirmed unto us by them that heard him;
4God also bearing them witness, both with signs and wonders, and with divers miracles,
and gifts of the Holy Ghost, according to his own will?"
This passage only refers to times previous to the moment in which it was written.
Do not be alarmed about the Markian passage. Some merely want to make it questionable as an inverted way to gain acceptance of the theory that the autographs were conflated by subsequent generation of copiers, thus casting doubt upon the Byzantine/Majority Textform to seduce supposed (prideful) "scholars" for the "older-is-better" but corrupted Alexandrian tradition.
I have no confidence in the opinions of those who would eliminate Mark 16:9-20, and am very suspicious about anything else they touch (which includes most of the "modern" versions and their proponents).