This is news to you? Any Catholic who obstinately denies defined doctrine becomes a heretic.
The early church Fathers did not teach this.
St. Irenus--Against Heresies--180 AD: "Where the Church is, there also is the Spirit of God, and where the Spirit of God is there is the Church, and every grace: for the Spirit is truth"
What Church Father ever said a Christian could choose which doctrines to believe or reject? That is Protestantism. Church Fathers fought wars over the purity of doctrine.
How does this address the original question..why did the church make a doctrine of the assumption and the immaculate conception if their doctrine only addresses heresies.. as I pointed out even The Catholic Encyclopedia admits that the first “genuine” written references to the Assumption come from authors who lived in the sixth to the eight centuries:
So why the doctrine on this?? Obviously it was NOT to address a heresy