I think that thoughtful people who disbelieve in free will recognize that this cannot be argued, but they can non-irrationally assume (or fear) that it is true nonetheless - and I think this is the real problem with this debate.
You cannot coherently argue that there is no free will, because in an universe where everything is determined by what went before, there is no such thing as an argument - I mean, the outcome of everything is predetermined by what went before, so what appears to be an argument is just more of the same cause and effect stuff.
To a determinist, the argument in favour of free will is a delusion just like they say that my intuition that I have free will is a delusion.
So, the belief that humans cannot really choose, but only believe that they can choose, is a belief that cannot be argued-for - not really.
However, it is possible to believe that the universe is totally determined, that there is no free will, no real choice, and that there are no such things as autonomy or agency whereby entities can be independent of the web of causality.
(Because that is what free will entails: it entails people are un-caused causes, un-moved movers - it entails that choice, action is not determined by what went before, but is autonomous from the preceding causes.)
So, a person may believe this, inside their heads as it were - believe that that is the way the universe is set-up; where everything that happens happens only because of what happened before; and that everything else (purpose, teleology, meaning, realtionships, knowledge...) are delusions which are themselves merely a consequence of the way things are set up.
This is, I think, the same phenomenon as relativism. The majority of Western 'educated' people nowadays are relativists - they explicitly repudiate moral values, absolute truth, objective beauty... but this cannot coherently be argued (because if 'everything is relative', then so is the claim that 'everything is relative).
Nonetheless, although determinism and relativism cannot be argued, they can be believed - more to the point - they can be feared to be true.
And I think this is the significance of these phenomena. People - en masse - indeed it is a defining feature of our current 'civilization' - fear that determinism is true (whatever they think about it), fear that relativism is true (whatever they think about it).
Our culture is in the grip of this fear. Our culture assumes that determinism and relativism are true - the assumptions are built-into public discourse.
Determinism and relativism are not things that people have inferred by logical reasoning - that makes no rational sense; nor discovered by scientific, historical or any other kind of empirical investigation - that makes no sense either.
(How could you 'discover' that the process of discovery was predetermined? Nonsense. How could you discover that science is relative?)
No - these things - determinism, relativism - cannot be inferred or discovered.
Neither are they natural or spontaneous beliefs: people are not born believing in relativism and determinism: quite the opposite! We are born spontaneously and naturally believing in absolute objectivity; and with a belief in our own free will, agency, ability to choose.
Everything suggests that they are planted by modern culture.
They are planted in the mind, they do not make logical or empirical sense - BUT they do cause fear, despondency, nihilism; because we fear they may be true yet we cannot prove to ourselves (or anybody else) that they are not true.
They do not make logical or scientific sense - but logic and science cannot get rid of them, because determinism and relativism destroys the validity of logic, and science lacks the capacity to influence metaphysics (science is within metaphysics - science cannot test metaphysical assumptions).
Determinism and relativism are ideas planted in the minds of Men by modern culture - as one might plant a cancer or an infection - and there they fester.
Once implanted they are hard to get rid of - people suspect, people fear, that these ideas may be true and they cannot prove they are not true.
So, there they sit, and grow and grow - destroying all purpose, meaning and relationship.
Ideas like determinism and relativism are a great way to destroy - wholesale.
They can destroy everything positive, everything good - including (eventually) all religions, ideologies, human relationships, possibilities for cohesive action.
They are a great way to make people afraid, depressed, despondent, anxious, unconfident, lazy, purposeless, directionless, short-termist and hedonistic, callous, self-indulgent and the rest of it.
Modern culture does this.
But why does modern culture do this?
Why would it be considered
desirable actively to plant such demoralizing ideas into people minds -to defend and propagate these ideas - ideas that tend to grow and destroy, while being irrefutable?
It does not make human sense!
I infer, then, that these ideas are not humanly motivated but have been strategically promoted, pushed out from from behind the scenes, by supernatural purposive evil.
In other words, it seems that these are demonic ideas - ideas which are actually created and disseminated on the basis that they are intrinsically and deliberately destructive. Destruction is the whole point!
A culture which deliberately implants and celebrates ideas like determinism and relativism does not make human sense; but it does make Satanic sense.