Quantum theory disproves it
Who are you to disbelieve in anything?
Free will only becomes important on a personal (I do x because it's meaningful to me) or social contexts (I'm responsible for consequences of x action).
I doubt the philosophers are trying to say anything about our day to day lives and that's where most of the opposition is coming from (ie no free will, therefore no meaning in life or responsibilities for anyone).
As you suspect, people discussing this misses out on how it's all relative, not so absolute.
However I don't think we're living there. We live in our own minds with a limited view and understanding, mostly dealing with social problems day to day, and emotions coloring that view however they see fit.
So IMO the "soul" and "free will" (or whatever other beliefs one may have) are ultimately metaphors for navigating the complex inner world. They can be very important/useful for the individual and society yet non-existent in the "objective world".
To me there's no contradiction.
There are knows: We have shared lucid experiences and we can share contemplations of such.
There are unknowns: What is consciousness, what happens exactly in brain in relation to outside (body, family, room, house, area, town).
It all seems interconnected to the point of break-down when not, for minds especially.
> But few people involved in the free will debate think that makes a critical difference. Those tiny fluctuations probably have little relevant impact on life at the scale we live it, as human beings.
Free will or no free will, is not the assumption in point 2 fundamentally flawed?
Quantum mechanics is surely at the heart of all interactions and so at some level is responsible for the ‘illusion’ making any difference between free will and predetermination unknowable.