As far as those who disagree, I would need references. One problem is that the evidence indicates the texts of the gospels, particularly the synoptic gospels, evolved, and were progressively edited and added to from ~50 AD? to their final form involving more than one author.
It is possible that the Gospel of John had one author, but the author is unknown, but traditionally the author is
John son of Zebedee, one of Jesus' apostles. Text analysis concludes that the text has gone through two to three revisions.