If you accept that cause/effect governs everything (i.e. each effect has a cause) then free-will (in terms of undetermined choice) can not exist, as to do so requires something to intervene in the causal chain - something that is not governed by cause / effect - which is contrary to the premise.
This is a logically valid argument.
The only question is whether the premise (that cause/effect governs everything) is true or not.
This is very nicely broken down. As far as we have been able to tell up until the last 80 years or so everything operates based on cause/effect, and the corresponding forces acting.
I believe this is where quantum mechanics enters the equation because simply perceiving has been shown to cause an effect in quantum experiments.
The world you see is nothing more than potential of the quantum world being actualized by continuous conscious interaction. You can train your conscious to actualize different potentials, hence the old adage "mind over matter." However you cannot actualize different potentials at once, and everyones conscious involved plays a part. The dominant conscious memes in a culture determine what potentials are actualized and consequently how the world appears to that culture. This is how the media works, it repeats certain ideas and values to you until your consciousness embraces it and accepts it as reality. It is hard to understand how you can direct your consciousness (and thus your reality) unless you have given meditation a serious try.
Your conscious is like many horses all tied to a knot in the center. Which ever horse you coax (ie either the negative or positive horse) will end up pulling you in that direction. This is why people inherently seem to be positive or negative, but really these people are choosing to be that way.
Meditation is the art of centering your mind so no horses are pulling, and suddenly you realize you can "choose" which horse you want to do the pulling.