But there is no reason why God cannot create beings with the capacity to make free decisions and at the same time know what decisions they will make. To say that He can't is to diminish His sovereignty simply because we can't quite grasp how it is possible."
I think 100%, each and every professing Christian, will agree that God has the capacity to create beings capable of making free decisions, i.e not predetermined by God or compatilism, and many will agree He did.
Likewise, I think 100%, each and every professing Christian, will agree God can know beforehand, what decisions we will choose to make given a circumstance. Thus Jesus can tell Peter that one day Peter will stretch out his hands and go where he does not want to go.
The real issues are simple, when God declares what will happen, that future happening is now predetermined. God will cause it to happen. Therefore He will not allow beings capable of making free decisions, to make any decisions that would prevent His declared happening from happening. He can create us with the capacity to make free decisions and then He can override us and cause us to make the decisions He desires, i.e. He can harden the hearts of people to prevent them from accepting the gospel for the purpose of spreading the gospel to the Gentiles.
When Jesus told Peter what would happen in the future, He might have been telling Peter what Peter would freely choose to do based on His knowledge of Peter's character and His foreknowledge that Peter would be anointed with the Holy Spirit. Scripture does not say. But what is certain, what scripture does say, is once Jesus told Peter what Peter would do, that happening was predestined, God had declared that end or future event, from the beginning, i.e. well before the future event. This has nothing to do with God supposedly looking into His divine crystal ball from "outside time" and everything to do with how scripture says God fulfills His prophecies.
So the real issues are:
1) Does God predestine everything? I say no, and that is the orthodox view. Hyper-Calvinism, exhaustive determinism, and closed theology is the unorthodox view in opposition. I say scripture says God causes or allows whatsoever comes to pass, so He does not predestine everything, and therefore is not the author of sin.
2) If God knows what we will decide, can we decide anything else? I say no. Therefore, we have no choice, we are like a person in a room with one door. We may walk in circles, stay for hours, or walk backwards, but when we leave, we will leave through that one door. That is not a choice, that is a future fixed in stone.
The opposing view is that God can look upon our free decision from outside time, as if looking at it after the fact, i.e. as history, and know what we freely chose to do. The problem with this "the time travelers God" invention is that it presupposes that God has created the future on the other side of the veil of time and therefore know it by looking at it from "outside time." If the future exists and is just waiting to be revealed by the veil of time, then the future exists and is set in stone.