One wonders how it was ever invented, in that case. Perhaps a common species of birds had a song that sounded just like “You-have-free-choice You-have-free-choice” and after early humans heard that song over a period of decades that’s what started the whole thing.
It’s no different to any other myth in this respect, we know of at least two reasons, one is to absolve God of responsibility for mans suffering and another is to justify retribuitive justice.
Seriously, if you believe what you’re saying then make a real (organized, step-by-step) proof of it.
I think perhaps you believe it’s impossible, They say you can’t prove a negative but I’ll have another go on the free will thread, as we’ve been off topic for some time.