On one hand, God is Omnipotent and Omniscient, all powerful and knows all.
On the other hand, we do have free will... how to reconcile these two seemingly contradictory truths is where we hit stuff like Calvinism and Predestination... Predestination is not true, as long as you have a breath of life you are capable of salvation, nobody is born damned, it is simply that God is omniscient.
Our Lady of Fatima said that WWII could have been averted, was she a liar? This alone destroys such false theology IMO.
Then you look at St Peter, Jesus praying for him in Luke 22:32, why this if everything is set in stone?
"Watch ye, and pray that ye enter not into temptation. The spirit indeed is willing, but the flesh weak." - Matthew 26:41
Why? If it's all predetermined from birth, what's the point? Is this a joke? He already knows and there's nothing St Peter can do to avert it according to these false ideologies? Why even get judged for sin if everything was predetermined from birth? If we don't have free will then it's not our fault.
As you can see, false understandings lead to erroneous conclusions.
God Bless