1)The free will controversy includes a logical problem.
There are many levels to look at phenomenon. As I am typing these letters, there are atoms involved. There are words, and there are ideas. You can look on different stages and details of what happens. Every way of looking depicts different phenomenons and details.
There is a phenomenon of something within the human brain that plays a role in making things happen. In a sense, this program is created by genetic instructions, outer experience etc. But at every given moment there is something in the mind that is part of making things happen. (another rather psychological controversy is how much is this program involved and how much are other processes, but this is an empirical issue which I am not handling here. See Bandura's chapter in the volume "are we free" references below for a presentation in favor of more free will in doing).
This program of dynamic in the human brain is influenced by endless factors, no doubt. No one claims it to be a pure soul that makes decisions. Now, there is a confusion about the levels of causation. The fact that there is a higher level of causes that influences the "self" program, does not means the self does not exists. It also seems reasonable that the self is having it own procedures now. Even if earlier these procedures and tendencies where coming from outer sources, they do exist now.
It may feel strange psychologically that what I call "my" self is created from outer influences. But this psychological discomfort does not reduce the existence of the self, it may merely reduce its aesthetic appeal. In a sense the effect comes from a naive psychological want to it to be purely "my", fully initiated by oneself. We are clearly strongly influenced from the outside at the origin. But now, we exist and we have an effect.
2) The ironic game of beliefs in free will.
The self acts differently when he believes or does not believe in free will.
In reality, the argument about free will is which belief to feed the "machine". It is not just about truth, it is about which aspect will be fed into the machine. Here one may want to ask what effect will this belief have vs. this belief. (There is interesting research in Baumeister laboratory showing that when people believe in free will, they are happier, more efficient at work and nicer towards others).
Ultimately, the sides fight on how the self will act and feel rather than just about a philosophical claim. Practically, they want the machine to act so or so.
One may talk about truth. But truth lies with both sides, since what matters is the meaning of free will rather than its technical (so called "philosophical" truth). Truth is how people understand and perceive the statement, rather than its legal meaning. Since most discussions of free will ignore the meaning problems mentioned above, the talk about truth is empty. Truth is with the ultimate meaning of what you talk about, not in being technically right but wrong in the implications and common understanding. (aside of that, having a better life and world is clearly more important for normal persons than "truth").
Bandura A. (2008). Reconstrual of "free will" From the Agentic Perspective of Social Cognitive Theory in Baer J., Kaufman J. C., Baumeister R. F. (Eds.) Are We Free? Psychology and Free Will New York, Oxford University Press.