Easily solved and explained as follows:
SCENARIO A:
Don't give them free will.
Make it impossible for them to prove that they don't have free will.
Then, give some of them the profound belief that they do have free will.
And, give most of them logic and reasoning, so they can argue about having free will.
SCENARIO B:
Give them free will.
Make it impossible for them to prove that they have free will.
Then, give some of them the profound belief that they do not have free will.
And, give most of them logic and reasoning, so they can argue about not having free will.
Either way, you get the same outcomes --
If this is a "bug": Debates about basic human design criteria, due to the absence of the original design documentation and an ineffective customer support help desk.
If this is a "design feature": A fascinating built-in propensity to understand oneself and discover the fact that humans are created according to an unfathomable supernatural design.