>>856308 (OP)
Plenty of early writers quoted 1 John 5:7 and it appeared in numerous Greek and other language manuscripts.
It is interesting that the very first thing you turn to in attempting to "prove" Arianism is this empty claim. Many supposedly orthodox Christians argue that its removal does nothing to change the doctrine of Christ or the Trinity. I am inclined to believe at least that much, as we see the Holy Trinity appear explicitly mentioned as a "mystery" in Colossians 2:2, as well as in many other places. However, I also strongly believe that Scriptural integrity being removed by the modernists in their falsely fabricated textual criticism, which, unlike that of the Textus Receptus scholars, is fraudulent and built on an actually very weak foundation, and unlike the scholars who worked with the TR the modern textual criticism insists that God failed to preserve His word accurately, is enough to shatter all belief in Christ and make one into an Arian or some other creature, despite their constant denials outwardly of this fact. Nay, they insist, their changes to Scripture alter no doctrine--- but I believe that is because they are already relativists and they believe in no doctrine at all to begin with.
Oh, but back to Arianism… It's wrong and unbiblical. Glad we could have this discussion, anon.