1) Jesus taught his disciples to emulate his own practices in their future ministry (e.g. Matt 10)
"It is enough for the disciple that he become like his teacher..."
2) Jesus made his public teachings known primarily (if not exclusively) via parables (e.g. Matt 13:34-35)
3) Matthew, as a faithful disciple, endeavored to emulate Jesus' own parabolic approach when authoring the first book of the Christian Scriptures.
It seems to me that modern Christians must reject at least one of these premises, in order to maintain that the Gospel According to Matthew may be firmly classed in the genre of biography rather than allegorical fiction or myth. Most likely, the third one, although it is difficult to see good reasons to do so apart from the obvious fact that the literalist approach generally prevailed over the symbolic and gnostic approach some eighteen centuries ago.
Certainly it would seem difficult to maintain that Matthew never incorporated parabolic pericopes into his gospel, given such passages as the apocalyptic saintly zombie bonanza and his wholesale midrashic borrowings from the books of Moses. Indeed, these passages never made any sense to me until I granted myself the leeway to read them as parables, at which point their meanings became quite plain.