The more words are changed or replaced, the more potential for ambiguity.
Ambiguity... that concept can be used for or against the KJV. Because the KJV is older and familiar to many, some argue that anything other than the KJV "causes" ambiguity. Same argument for variant translations of individual words, as given in footnotes... which some KJVO proponents decry as unnecessary or even evil. This is invalid given that the 1611 KJV had footnotes with variant translations.
There is often more than one word in a given language which accurately translates a single word from another language, so it is quite legitimate to use a different word in certain cases. It is not valid to claim that a passage translated slightly differently is "wrong" on this basis alone. Also, words may not have single-word equivalents. Greek has "wise" as a verb; English needs "make wise".
When the KJV is upheld as the standard against which newer English translations are compared, some will say it is "better". However, when both newer and KJV are held against a common standard of the body of manuscripts, the comparison of newer against KJV collapses completely. If the KJV-only proponents could understand and accept this logic it would undo much of the confusion and argument.