@Olivier5,
Olivier, I think I have found the answer to the stubbornness of the predeterminsts. It's simply caused by their belief in religion.
I have observed it in my siblings; they are all christians married to christians. I am an atheist married to a buddhist.
Their belief in their religion is sacrosanct. Nothing will change their minds.
No amount of explaining the why's of religion(s) is useless. They will never change their minds. NEVER. They will take it to their graves.