Praise the Lord, if I had to pass a theology exam I would be lost for sure. :)
It seems to me that the argument about predestination and who the author of sin is are linked. In both cases God knows from before creation who will do what. If not then God is waiting and reacting to His creation not knowing what will happen.
Why is it so wrong for God to be the author of sin?
“Why is it so wrong for God to be the author of sin?”
That is usually interpreted, I believe, as meaning God is the CAUSE of sin. In a deterministic theology, God makes people commit sin, then judges them for doing what he forced them to do. That is like beating a dog who had diarrhea while shut up in an apartment. The final straw that forced me to leave the Baptist Church I had been a member of for 5 years was when I was told that God decided what sins he wanted me to commit and then made me do them. FWIW, I believe most Calvinists reject that idea, although I don’t know enough Calvinists to say for certain.
OTOH, if God gives us the right to make real choices, then we sin because it is our evil nature at work. We are slaves to sin, freely rolling in our vomit, so to speak. We sin because we like it, and because we cannot free ourselves. But Jesus came to set the captives free, and that is the Good News.
From a more Arminian position, God created a world where he knew there would be sin, because it also gave us the freedom to become his sons and he considered the end worth the process. He wasn’t surprised by the Fall, but had already planned for Jesus to rescue any who believed the promise of God.