"For there are three that testify," 1 John 5:7 NET
"For there are three that testify:" 1 John 5:7 ESV
"τρεῖς εἰσιν οἱ μαρτυροῦντες," 1 John 5:7 SBL
"οτι τρεις εισιν οι μαρτυρουντες εν τω ουρανω ο πατηρ ο λογος και το αγιον πνευμα και ουτοι οι τρεις εν εισιν" 1 John 5:7 (Scrivener) TR 1894
"For there are three that bear record in heaven, the Father, the Word, and the Holy Ghost: and these three are one." 1 John 5:7 KJV
It is obvious which versions follow which Greek renderings, above. Even if you don't read Greek, it is very apparent by its length that KJV follows the TR (and a few other corrupted later manuscripts.)
Why corrupted?
First, the longer version is based on scribal additions, placed in the margins. The next generation appeared within the text, rather than as a margin note.
Second, the longer version does not appear in any of the writings of the early church fathers. This is important, because, except for a few disputed verses, all the other verses of the NT appear somewhere in the early church fathers. During the Arian controversy, concerning the deity of Christ in the 3rd century, all the NT verses were scoured for proof of the Trinity. The later, longer version would have provided definitive proof of the Trinity, and hence, the deity of Christ, but this verse did not exost in th 3rd century. (Certainly, proof of the Trinity is found throughout the NT, and foreshadowed in the OT, but NOT this verse!)
Third, if something suddenly appears in a 16th century version, was it removed by later scholars, such as Hort and Westcott and SBL, who could not find it in the first 15 centuries of Christianity, more or less, (Vulgate cl , arm mss, 2318, 221 vr, have it added,) or was it added later, then encoded in an English version which gained prominence for 4 centuries?
I'm sure the answer was that it was added much later, and the popularity of the KJV gave rise to many thinking it was in the original manuscripts.
The fact is, the so-called "majority" texts are the majority or there are more copies than other versions, because the Byzantine Empire kept its Greek, and monastic orders arose to copy the earlier versions. Monks copied copies or copied or copies, and transcribing errors appeared which were incorporated into the Greek manuscripts. There are many examples of notes in the margins, added by scribes, then being incorporated into the text in the next generation. I have seen photos of these notes in a Greek text book, then the next generation incorporating it. (See Kostenburger.)
As for the volume of Greek texts, if they belong to the same family, in fact, they are not really 200 manuscripts, (to throw out a number) but 1 manuscript of that generation, copied 200 times.
Further, the argument that the Alexandrian manuscripts are heretical is based on flimsy logic. Yes, SOME of the Alexandrians, like Arius were heretical. But the bishop of Alexandria, Athenasius opposed Arius, and took the whole debate to a church council in 325 AD. In fact, that church council affirmed the Trinity and the deity of Christ, using versions which do not include the spurious and much later addition which the KJV copied.
Just because there were heretics, that didn't make their manuscript heretical. Just as people come into CC all the time, declaring some heresy or other, using the KJV, that doesn't make the translation heretical. On the other hand, the New World translation of the JWs has actually changed the words of the Bible to say something it never said in any manuscript. That is a heretical version.
Finally, Erasmus upon whose Greek version the KJV is based, to a large part, did not want to put that spurious longer verse (1 John 5:7) into his translation. The Catholic Church demanded he keep it in, despite the total lack of manuscript evidence to support it. The RCC wanted it there, because it was an easy verse to support the Trinity. Erasmus was not allowed to publish his translation and have the Imprimatur approved seal in 1516. Another version was being prepared, he rushed his version to press early, getting more sales and obeying the RCCs dictum! Profit motive in a priest. (There were other errors and problems with his version, which the KJV also copied!)
PS I do totally believe in the Trinity, but I would never support my belief with the longer version!
There is a huge list of early Greek manuscripts that do not contain the longer verse, including, aleph; A; B; 048; 33; 81; 322; 323; 436; 945; 1067; 1175; 1241; 1243; 1292; 1409; 1505; 1611; 1735; 1739; 1846; 1881; 2138; 2298; 2344; 2464; Byz; it,p; vg ww, st; syr p h; cop sa, bo; arm mss; eth; geo; slav; Clement; Ps-Dionysus; Rebaptism; Ambrose; Augustine; Quodvultdeus; Facundus.