The main argument of those who think the book was written by another John is that The Revelation is written in a less polished form of Greek. One answer to this is that John was unschooled- Acts 4:13, "when they saw the boldness of Peter and John, and perceived that they were unlearned and ignorant men . .

Facts and logical constructs

I John is the source for the oft-cited phrase: "God is love" (I John 4:8). The author likes that phrase enough to repeat it later in the same passage (v 16).

It is one of the few phrases in the Bible set up as a copula: "God is X." So it's attractive to those trying to answer the big question of the nature of God: "Let's see if the Bible anywhere gives us a straightforward answer to the question, 'What is God?' Ah! Here's a place."

So far, then, so good.

The gospel is like the life-saving penicillin which is only effective when it is kept pure. Heresy is akin to the diluted vaccine and causes irreparable damage, in some cases accelerating the debilitating effects of sin, resulting in would-be believers becoming the spiritual equivalent of brain damaged children; in other cases, leading to their spiritual death.