In the Christian worldview the concept of human includes an immortal soul, which is created by God and has free will. Free will - a person's ability to be cause for their actions and decisions himself. Possessing free will, a person can make an responsible choice between good and evil. In fact, without the recognition of this ability of the person the religion makes no sense.
The atheistic conception of the world offers that there is no God, gods, angels, spirits, souls, etc. For the consistent and uncompromising atheist only matter is real. Cases where an atheist believes in something spiritual, but does not want to listen to the priests, will not be considered.
Matter has certain properties. Water boils upon heating and upon cooling freezes. A situation, where the water is heated and its water soul, possessing free will, opposed to this, and the water freezes to spite us, is absurd. Living matter has also defined and predictable properties. The virus moves along with the carrier medium coming into contact with the cell and penetrates into it. He does not have free will to decide - to penetrate him in a cell or not. In unicellular same no free will - they absorb nutrients and are divided according to the capacity of the organism. The same situation with cockroaches - they just react to changes in the environment - the smell of food, they went there, felt the danger - fled under the plinth.
The atheistic worldview man is as responsive to changes in the external environment and changes in the state of his body, in accordance with his existing installations. His decisions and actions due to his existing IF-THEN statements. These statements a great many, they have some weights, etc., so the person creating the illusion that he makes decisions in accordance with his free will. But this is an illusion - a man is just a very complicated intelligent agent, biorobot. You will not say that those balls that chase the protagonist in the game Pacman have free will? This program of action result. All the people - it's pacmans.
With the idea of lack of free will is closely related to the idea of determinism - universal predestination. If you know the applicable laws of existence of matter and its state, it is possible to predict its state in the future. There is a philosophical concept – the Laplace’s demon, which, to put it in modern categories, is a super computer, which you can use to process information about the current state of the material world, and to know that John Doe from New York after 3 years 5 months and 4 days to marry Jane Doe from Nevada, as at 1 year, 2 months and 6 days, they randomly met in a café. Human life - a game in which we are no more than puppets.
In all fairness, it should be noted that there is an opinion, what Schrödinger's cat can confuse the Laplace’s demon ‘s cards. In our world, there's no true randomness. If we toss a coin, it does not fall randomly - it falls under the laws of physics, and its fall trajectory can be calculated. But it is believed that there is a real chance at the quantum level, and quanta in the right place of the human brain can introduce an element of randomness in its decisions. But in any case, it will not be the result of man's free will.
So, free will is not in the material world, determinism is likely to have, but maybe he sometimes corrected by random events.
The fact that atheism requires a person to admit that he is not his own master, is the doctrine of atheism that atheists are not used in the missionary books. The reason, why people do not appricate this side of atheism is not surprising. The idea of a human unfree will contrary to its intuitive notions about themselves. From that moment the man becomes aware of himself, he thought of themselves as the owner of free will, and believes that he and others are responsibly for their actions.
In addition, the atheistic idea of human unfree will contradicts to all of the pathos of Western culture - a man in it appears as the creator of his own happiness. Atheistic materialism tells us that a person becomes a Nobel laureate or a hobo, not because he had taken in his life a number of his own decisions, but because it was determined.