Both the KJV and the Modern Bible Versions cannot be God's pure word; logically, either one or the other has to be corrupt.

From Crowned With Glory, by Dr. Thomas Holland:

p. 14. One notable distinction deals with the number of verses contained in the Textus Receptus that are not contained in the Critical Text, and therefore do not appear in most modern versions based on that text.

[The Textus Receptus is the Greek text that underlies the King James Version; the Critical Text is another set of Greek manuscripts that underlie the modern Bible versions.]

This, of course, does not prove a certain translation correct and another incorrect. These verses are Matthew 17:21; 18:11; 23:14; Mark 7:16; 9:44, 46; 11:26; 15:28; Luke 17:36; 23:17; John 5:4; Acts 8:37; 15:34; 24:7; 28:29; Romans 16:24; and 1 John 5:7. Additionally, Mark 16:9-20 and John 7:53-8:11 are contained in the majority of Byzantine manuscripts and the Traditional Text. However, most Alexandrian manuscripts do not contain these verses, and therefore are so noted in the Critical Text.

[The Byzantine manuscripts make up the general class of Greek manuscripts the Textus Receptus is based on, that underlies the King James Bible, and the Traditional Text is another term for the Textus Receptus which is derived from the Byzantine group of manuscripts. The Alexandrian manuscripts are those the modern Bible versions are based on, and the Critical Text is the specific version of those manuscripts that is used for the translations.]

This leaves the Christian who believes the commands of Scripture in a dilemma. Three times the Bible warns against adding to or taking from the word of God (Deuteronomy 4:2; Proverbs 30:6; and Revelation 22:18). Either the Greek texts that remove these passages are corrupt or the Greek texts that add them are corrupt; one cannot be biblical and believe that both textual lines are pure.

Hard to dispute that, it seems to me.