You are free to believe what you wish to believe.
I do not know if what you think Augustine taught about predestination is what he actually did teach, but I will not be researching his teaching in order to find out since it does not matter in order to make my own point.
Augustine was free to express his opinion just as his Catholic contemporaries were free to express their opinions about predestination since the Church had not made any formal pronouncements about it.
However, the Church has since ruled that double predestination cannot be believed by Catholics.
Fr. Ray Ryland writing in
Catholic Answers magazine explains the Catholic teaching about
Predestination:
"The key to the doctrine of predestination is given in the Catechism of the Catholic Church:
“To God, all moments of time are present in their immediacy. When therefore He establishes His eternal plan of ‘predestination,’ He includes in it each person’s free response to His grace” (No. 600).
In other words, what God foresees and wills takes into account how we use our freedom in responding to Him or in rejecting Him. God’s foreknowledge in no way detracts from our freedom.
Sacred Scripture assures us that “God our Savior … wills all men to be saved and to come to knowledge of the truth” (1 Tm 2:3-4). Moreover, Christ Jesus “gave himself as ransom for all” (1 Tm 2:5).
The Church teaches that God “predestines” us both to good works and to eternal happiness in heaven. That is His plan for our lives. We are free to reject Him, but even our rejection itself is somehow a part of God’s overall plan.
God always holds out the grace of conversion to sinners, even as He foresees who will reject that grace and be forever lost. The Church also teaches that apart from special revelation no one can know with absolute certainty whether he or she belongs among the elect in heaven.
You should ponder Romans 8:28-30. It is Scripture’s fullest statement of the working of predestination in the lives of the elect. “Elect” refers to those persons who will respond to God’s infinite grace. And remember: The freedom of the elect will always be unimpaired."
It is not necessary to destroy “some” in order to save “others/many.” This is incorrect thinking. God is almighty/omnipotent. The only things that God cannot do are things that are against His Divine Nature. In other words, God cannot do evil because He is all good.
We will have to agree to disagree on this. I do believe the Church’s teaching on predestination.
After all, Jesus founded His own one, holy, catholic, and apostolic Church and He promised to lead it into all truth by the power of the Holy Spirit and He promised to be with His Church always until He returns. The Holy Spirit prevents His Church from teaching error in matters of faith and morals and Scripture interpretation in its official pronouncements. He promised that the gates of Hades would never prevail against His Church. If His Church ever teaches error, then the gates of Hades will have prevailed. Jesus cannot lie so this means that His Church cannot ever teach error.