It is fairly obvious to most people that reason is not the only access to knowledge (although in my enthusiasm for science I personally tend to forget this at times).
For example, can reason tell you what the experience of love is like, or of exhilaration, or of fear, or of faith or of despair or of disillusionment or of indignation or of justice or of perception or of reasoning? At most it can hypothesise how these come about or tinker with drugs and neural stimulation to modify them but the actual existential experience of these is beyond the gambit of logical analysis or experiment. (see also Reweaving the rainbow).
For this we can be grateful. If the natural world is all there is, then decision making can be nothing but a product of the natural world and nobody has free will, or, ultimately, any moral responsibility for any action. The decisions of a serial killer can be attributed to the atoms and force fields in his brain-body system, in his parents, in the people around him, in the ancestors of these and in the natural world going right back to the creation of the universe – or, if you believe in an eternal natural world, to an infinite number of past events which have occurred an infinite number of times and which will repeat themselves an infinite number of times in the future.
I have not knowingly met a person who claims he has no free will. We know it is not an illusion. It is as basic as believing that we exist. Anyone who considers himself or herself as devoid of moral responsibility cannot function as a human being in a human society. In effect, this means that nobody can really claim that the material world is all there is.
Author, 2077 AD