It is a sad irony that many of the Christians who champion a high view of biblical inspiration mindlessly use the most corrupt translation based on later error-prone manuscripts. For a list of some of the bogus verses later inserted into the text, see:
Translation errors and forgeries in the Bible
I will focus on the most egregious error, the contrived ending of Mark (16:9-20). NT scholars are unanimous in their verdict that this text, missing in early manuscripts, was added later to compensate for the awkward ending of the original text, which lacks a resurrection appearance of Jesus and which ends by lamenting that the women at the tomb disobeyed the 'young man" in the white robe's instruction to tell the disciples that Jesus is risen and will appear to them in Galilee. In fact, one ancient manuscript of Mark even identifies the forger as Aristo of Pella (c. 150-165 AD). Thus, later Greek manuscripts invent other endings of Mark to remove this Scholars also agree that the style of the Greek of 16:9-20 differs to greatly from Mark's to be authentic.
But let's consider the harm done by the words misattributed to Jesus in 16:17-18 of this spurious interpolation:
"17 And these signs shall follow them that believe; In my name shall they cast out devils; they shall speak with new tongues; 18
They shall take up serpents; and if they drink any deadly thing, it shall not hurt them; they shall lay hands on the sick, and they shall recover."
Many KJV Only Appalachian Christians have died and caused other believers to die as a result of the underlined challenge in this text. It is unthinkable that Jesus would identify as a badge of true believers that they would handle deadly snakes and drink deadly poison as a test of their faith. Why would anyone drink deadly poison? This bogus promis is a misapplication of accidents like that noted in Luke 10:19). These "signs" are in any case too bizarre to be credited to the real Jesus.
In the 1600s, the KJV translators lacked access to the earliest and most accurate manuscripts. Many manuscript discoveries have happened since then, giving birth to the science of Text Criticism. This science collects and compares all biblical manuscripts, groups them into families by text type, region, and date, and discovers when and where the thousands of errors have crept into the text. Yet many evangelicals lack the integrity to read any scholarly book on Text Criticism to see how compelling the evidence really is for the modern critical text of the Hebrew and Greek Bibles. Instead, they prefer to impute ungodly liberal motives to scholars who revere the original word and are just trying to recover it as purely and accurately as possible. So when preachers I don't know use the KJV in their preaching, I quickly turn off the radio or TV or stop attending the unenlightened church in question--and that comes from a man who, as a boy, used his paper route money to buy an expensive Thomas Chain Reference KJV Bible, so I could read it from cover to cover. I was hungry for the truth of God's Word, but learned, only later, that this Bible translation was sadly flawed.