We need the bible.
The bible often used a vinyard as an analogy.
Grapes grow on two year old wood. Year one just leaves and a new shoot. Fruit year two, then the branch should be pruned off.
But the stem is maintained and fertilized. That is the Bible and tradition. You injure the stem and the whole plant dies.
Spong is wrong. Protestantism could not have formed except in relation to RC corruption, and PC could not have formed except in dialog with superstitious Christianity.
We should recognize the Hegelian dialectic and use it to encourage new thought and prune the old carefully but leave the central organization.