Some (unfairly) single out the New International Version (NIV) as a particular culprit and draw a line to the fact that the NIV publisher Zondervan is now owned by the secular publisher Harper Collins and there is thought that Harper Collins wishes to alter the scripture.
The verses in question are Matt. 17:21, 18:11, 23:14, Mark 7:16, 9:44, 9:46, 11:26, Luke 17:36, John 5:4, Acts 8:37, 15:34, and 24:7. However, it is important to note that biblical scholars have for a long time questioned these passages. This is due to the fact that we have many more copies of manuscripts today than were available in 1611, when the King James Version was translated. We are better able today to identify which of the manuscripts was copied earlier and which came later and which was copied from what. Remember, we do not have any of the original documents (autographs) of the Bible, we rely on copies made by hand over the centuries.
By in large these copies are remarkably accurate and identical. However, scholars note that over the centuries of copying there were words or phrases added to some manuscripts. All of these changes are minor and none of them influence any doctrine or belief in any way. It may have been that a well-meaning person copying a passage felt that the previous copyist had omitted what should have been there and added some phrases. With our greater ability to trace these changes due to increased evidence we can determine to a finer degree today, if a verse actually belongs in the text.
Seen in this light, calling for the sole use of the King James Version is in fact a step away from biblical accuracy not toward it. However, your modern translations do not all treat these verses the same way. Here are some of the differences I have noted.
1. 1984 version of the NIV has all the above verses footnoted in the text the with verses not shown in the text but completely written out in the foot note.
2. 2011 version of the NIV has all of these verses footnoted, but not written
out in the text or the footnote. When the verse is a duplicate of another text in scripture the reader is informed of that duplication.
3. The 2001 ESV, which is noted for its Greek/Hebrew accuracy, omits the verses from the text and writes them out in the footnote on each occasion.
4. The 1982 New King James leaves the verses in the text and footnotes the fact that the earliest manuscripts omit these verses.
5. The 1611 King James Version leaves them in the text with no reference, however modern publishers footnote some editions saying that the early manuscripts lack some of these verses.
Probably one wrinkle in this discussion today is that many of us read our Bible on devices. I have found wide variation in the practice of e-versions regarding how they handle this issue. Most follow the practice of the translation they are using as noted above, however it is often difficult to follow and find footnotes on these e-versions.
Bottom line, it is as conservative Biblical scholars do the hard work of textual analysis that reliability of the Bible is enhanced not threatened. They are uncovering wording that gets us ever closer to the originals and we must not hold on to phrases and word choices that are familiar simply out of love for familiarity, rather we must always seek accuracy.
His and Yours,