All you've done is pushed the question back a stage. Why should they consider spoken language primary? (Not to mention that many of us don't.) That it's older is insignificant; so often age does not equate to authority, or even vice versa. And for every anecedote extolling the spoken word there's another in the opposite direction. The Bible as the written word of God. Authoritativeness described as "carved in stone." Etc.