Those who hold to materialist theories such as Democritus in ancient Greece, E. O. Wilson in biology, and B. F. Skinner in psychology would argue that free will is an illusion because we are formed not by our free-will choices, but instead by forces that are strictly composed of matter such as atoms colliding or natural selection, or by social forces outside the individual person such as economic structures or rewards and punishments. See Consilience, by E. O. Wilson, 1999, New York, NY: Vintage, and Beyond Freedom and Dignity, by B. F. Skinner, 1971, New York, NY: Bantam.
I acknowledge that matter and social forces influence us, but they alone do not or even primarily shape us. If there is no free will, then you cannot say whether one thing is morally right and another morally wrong. If you reflect on it, you cannot say someone did wrong, moral wrong, if he is not responsible for his behavior. The legal system, for example, implicitly rejects materialism every time it says, “The defendant is guilty.” The defendant is not guilty if his genes or the principles of operant conditioning made him behave as he did. Would any materialist continue to be a materialist if his or her daughter was raped and the defense attorney said, “Rape is not morally and legally wrong. Society reinforces men for being aggressive, and he was only responding to this conditioning. My client therefore is innocent of all charges, and I ask dismissal of them all”? Either you accept free will as legitimate (and morally condemn rape, for example) or you lose your moral voice in standing up against moral atrocities.
Footnote 3, Chapter 1, The Forgiving Life by Robert Enright (APA Books, 2012)