The concept and the thing conceived of are two different things. Sunrises did not cease when heliocentrism began. That someone conceptualises something in a way that can easily be knocked down does not mean that there was nothing there. Dennett makes this point in his review.
Then you mean a different thing by "free will" then me- I was referring to free will in the popular conception.
I've raised arguments for philosophical scepticism before, which have mostly been argued against in a Popper-esque manner of arguing that even if we don't know anything with certainty, we can have legitimate knowledge on probabilities.
The problem with this, however, is how you answer a sceptic about the notion of probability having a correlation with reality. Probability depends upon axioms of probability- how are said axioms to be justified? It can't be by definition, or it has no correlation to reality.