There is no evidence that we are anything more than the atoms we are made of, and if we are nothing more than the atoms we are made of, then our every thought is a physical (atomic, chemical, electrical, quantum, etc.) reaction.
Assuming there is no random element to the physical reactions we call thought, it would still be true that predicting the physical reactions we call thought is impossible – for all practical purposes – today. However, as technology advances, it will increasingly enable us to predict the physical reactions we call thought, but probably never with perfect accuracy. Also, there may be a random element to the physical reactions we call thought, in which case, predicting thought with perfect accuracy would never be possible.
Free will is thus an illusion – but an illusion so close to reality that, for all practical purposes, we do have free will.
Why bother discussing the reality of free will then?
Suppose we were intellectually lazy and thus the only reason we didn't allow punishment for crimes before they were committed was because we believed that free will was real – just because it seemed real. Then our intellectual laziness would make us vulnerable to progressive tyrants and their scientists who claimed otherwise – because they want the power to punish people for crimes not yet committed. Whereas, we who have considered the reality of free will can say that we trust no one to predict the actions of others whether free will is real or not. We trust no one to punish others for crimes not yet committed.
Like Free Speech, Free Will is a useful principle.
Although we know that some speech must be better than other speech, we also know that no government can ever be trusted to promote or censor any speech.
Likewise, although we know some people will commit crimes, we also know that no government can ever be trusted to reward or punish us for behavior not yet performed.
Just as we believe:
that government is best which operates as if all speech were equally good,
we also believe:
that government is best which operates as if free will were real.
Throughout history, those progressives who claimed to have a better way have proven to be wrong – and evil.