Like most people, I am not a fatalist, or I'd lie in bed all day hoping for my "life path" to bring me good fortune. Similarly, any stated fatalist with any ambition to do anything is a hypocrite. Here's why a purely materialistic view of the universe is at odds with free will aka purposeful self-direction.
Assuming all goes as planned, the last domino is destined to fall as soon as the first one is pushed. If the laws of physics were less rigid, one could not predict this.
Assume that all the laws of physics are perfectly rigid; are we not like dominoes whose actions were set by the past? Taking the view of a purely physical universe which follows purely physical laws consistently, there is no room in a purely physical brain for spontaneity.
Or consider a universe where the physical laws are not perfectly consistent. Here, a variation in one or more physical laws causes one domino to resist falling. In such a universe with only partial causality, still no mechanism for free will exists. In fact, such general randomness would be an impediment to free will.
The materialist view assumes that our intentions are generated by the brain and in the brain, in other words, thought is the BYPRODUCT of physical hardware processes, not the DRIVER. If true, then free will must be an illusion.
Conversely, taking the view that thought is the driver of activity in the brain, the seed of consciousness must be elsewhere and any study of brain activity will yield limited insight into how we make choices.
What if the brain drives itself by random mechanisms as a computer generates random numbers? Then I guess we would have random will, but not free will.
Some people have suggested that the unknowable future provides a mechanism for free will. The untrackable nature of any event and it's causal events and their causal events, etc. creates what appears as randomness. If somehow all events and their interactions could be tracked to predict the future, then it would be plain old physics. Neither apparent randomness nor plain old physics provide a mechanism for free will.
So how do we make the case for free will aka purposeful self-direction? Enter the SOUL. Only an energy operating outside the material realm could override the dominoes of destiny.
To accept free will therefore is to accept the soul, which must operate in a non-physical domain as the self-directing force, or as part of the self-directing force, distinct from the brain/body, while linked to the brain/body. The implications are not necessarily theistic, science might explain the soul some day.
Materialists must live with the logical implications of a purely physical cause/effect reality. They cannot take credit for their own accomplishments as they are merely observing destiny unfold. They must forgive all evil-doers as actors following a fixed script; if choice is an illusion, morality is irrelevant.