King James didn’t alter the Bible. He didn’t even want there to be a new English translation of the Bible. It was a bone he grudgingly threw to the Puritans in Parliament who wanted an English Bible, and he threw it because he didn't want the church to get saddled with an English translation of the Calvinist Geneva Bible by default.
Though the Puritan translators wanted to translate key Greek words in ways favoring their ecclessiology — e.g., translating episcopos as “overseer” instead of “bishop”, presbuteros as “elder” instead of “priest”, and ecclessia as “congregation” instead of “Church” — King James insisted that they use the traditional terms to translate them, i.e., he kept them from changing anything.
The KJV was an absolutely faithful attempt to render the best Greek and Hebrew texts then available into the then popular tongue of the English people. There was nothing shady about it.
The KJV was never authorized as a theological source: actual theology still had to be done from the original language texts. The KJV — like all other translations — was ONLY for devotional and liturgical purposes i.e, for the benefit and instruction of the masses who did not know Greek and Hebrew.
The KJV was created to be the standard authorized version for the Church of England … which effectively became the Church of the British Empire and the (Protestant) English-speaking world. It remained really the only Protestant-ish English version until the mid 20th century when the by then archaic language was putting many people off and creating confusion, producing a broad push to produce new translations in contemporary English. Revisionists, reformers, and revolutionaries — both left and right — jumped on the opportunity to produce translations more to their liking, spawning a rash of new English translations. (All the generally respected ones — e.g., the NRSV, the ASV, the NIV, the NASB, the NKJV, and even the NLT — are faithful attempts to properly translate the received text, and the differences between them in terms of doctrine, faith and morals are insignificant from a non-Christian perspective.)
Many (quite reasonably) preferred the poetry and eloquence of the King James. Many more had sentimental attachments to its phrasing of key verses — e.g., …
“And you will find the baby wrapped in swaddling clothes and lying in a manger” vs. “And you will find a baby wrapped in pieces of cloth and lying in a feeding box,” and …
“And why take ye thought for raiment? Consider the lilies of the field, how they grow; they toil not, neither do they spin: And yet I say unto you, That even Solomon in all his glory was not arrayed like one of these,” vs. “And why do you worry about clothes? See how the wild flowers grow. They don't work or make clothing. But I tell you that not even King Solomon with all his wealth had clothes as beautiful as one of these flowers.”
Which would you rather hear from the pulpit?
The Christian equivalent of Birchers (and many of them were also actual Birchers) saw in every modern English translation a Communist plot to subvert Christianity (to be fair, not without some justification due to some translations). These became the core of the King James ONLY movement.
