The attempt to "adulterate" scriptures took place even before translations were made.
To adulterate means to change some of the meaning in the scriptures in some subtle way.
Between the death of John the apostle and the reign of Constantine, a number of groups started to corrupt scriptures, saying they were "correcting" them.
Even Eusebius (who lived in Constantine's time) and who did a bit of "adulterating" of scripture himself, was appalled by some of the manuscripts being passed around. He wrote in his ' Church History, Book five, Chapter 28
"They (a group who denied the divinity of Christ) have not been afraid to corrupt divine Scriptures, they have rescinded the rule of ancient faith, they have not known Christ...they corrupt the simple faith of scripture and claim to have corrected them. That I am not slandering them anyone will learn who compares their writings, which are in great discord, for those of Asciepiades do not agree with those of Theodotus. Many manuscripts are available because their disciples zealously made copies of their "corrected" though really corrupted--texts."
The early church already had a basic (though there were still some disagreements on a couple books) New Testament prior to 312 AD. And also corrupted manuscripts were already floating around before Constantine became emperor.
When Constantine became Emperor, and accepted Christianity in 312 AD, he found numerous factions within Christianity, and forcefully tried to consolidate Christianity. One thing he tried to do was to adopt a "standardized" bible. But in doing this he combined and blended the various corruptions along with the true.
Basically there were three different scriptures each claiming to be the correct version.
One was the wide spread Asia Minor manuscripts (generally known as the Byzantine/Syrian or Received Text). Another was the western text, and the third the Alexandrian or Egyptian text.
Constantine orders 50 manuscripts of this "standardized" Bible.
A number of scholars believe the Vaticanus, and Sinatic MSS were from this 50.
Yet, these manuscripts did not flourish and spread far and wide.
The Christian people clung to the Received Text which remained the dominant Bible in the east, in Northern Italy and southern France and even in Celtic England.
The Waldensies and similar groups throughout the Roman world, had the Received Text Bible in the old Roman/Latin language, as this was the language they spoke.
It was years later (380-400 AD) when Jerome developed the Vulgate -- also in Latin, but a "low Latin" which differed from the Received Text not only in style but also in doctrinal accuracy. This later became the authorized Bible of the Roman Catholic church.
As centuries passed the old Latin died out as a common language, and soon the only Latin still used was by the church and the universities.
When the Reformation began and the printing press was invented. Brave men, in spite of threats from Rome, began to translate the Bible into the language of the people. They used the Received manuscripts, not the Vulgate and it's imperfect manuscripts.
It's not the fact that our Bibles are translations that is the problem, the question is -- what is their base?
Just like Wycliffe, Tyndale, Luther saw a need for the Bible to be in the language of the people -- that is still true today, and newer translations often bring out meanings that are hard to see in the more archaic language of the KJV.
However, for doctrinal study I want a Bible based on the Received Text, not on adulterated manuscripts. And for that the KJV is the best English Bible