Well there's your error right up front! Free will affects how such a person would react to their 'inputs.' Try encountering a dozen people at random one at a time. Give them the 'input' of saying 'Hello?' to each. Are their 'outputs' the same? Did their free will have any effect on said 'output?'
Gee, that was easy.
Or is causality only occasionally regnant?
--Boris