Free will vs Deterministic vs Randomness
In order for free will to exist, a person has to have the ability to make a choice — and this means that the future can’t be determined. So most theistic religious folks out there who believe in an omniscient “God” who knows the past, present, and future — demonstrate that free will can’t exist — due to this future being known. If this “God” doesn’t know the future, then that “God” fails to be omnipotent and by definition, fails to be “God”. Ironically, it is these same religious folks who have no choice but to believe that free will — even though true free will’s existence would contradict\ the very idea of an all knowing “God”.
Religion aside, in order for people to believe in free will, they have to agree that the world is at least adequately determined. If everything was random and unpredictable, then the choices that you think you make or the actions you perform would be inconsistent with each other. Paradoxically, that very determinism implies the absence of free will, for the more deterministic your actions become, a more fixed path is set and alternatives disappear. On top of this, uncertainty or indeterminism (currently proven with strong evidence in quantum theory) suggests that at the most fundamental level of existence, matter/energy behaves in a random manner (no 100% predictability). Unfortunately, this just creates another mechanism for lack of free will, because randomness is still something out of our control. So technically speaking, the fact that the universe operates under either determinism, or indeterminism, or a combination of both — implies that the universe operates in a way that eliminates free choice altogether.
To summarize, people are products of their genes, environment, and chance(randomness) — thus no free will.