Atheism is one thing: A lack of belief in gods.
Source: American Atheists
Is atheism a worldview? Yes. It answers the basic questions which any worldview answers. Where did I come from? Who is in charge? What is the purpose of my life? Where am I going once I die?
How one answers these basic questions of life can set the trajectory of how one derives their ethics and purpose in life. In an atheist worldview the individual makes themselves god since they determine their own destiny and ethics. They are not accountable to a higher standard of morality since they are the highest standard determining good and evil. So, the ramifications of an atheist worldview can have major consequences to the community in which they live, especially if they live out what they believe to be true in the actions of the government.
A good example of how this faith works itself out is seen when we consider the value of a human life. If you don't believe there is a god then the logical conclusion is that humans have no intrinsic value other than whatever pragmatic value they can provide for the atheist. Whether the state or anyone else murders another person has no real bearing on whether the taking of life is moral or not. In an atheist worldview there is no such thing as a universal standard of morality. Everyone decides for themselves what their own morality is since there is no authority outside of themselves to determine what is ethically right or wrong.
In contrast to this view of ethics a Christian worldview considers every human being worthy or life and protection against a tyrannical state or a murderer that would rob them of their life. All humans are valued solely for the reason that they are created in the image of God. This perspective leads to a restriction on the state's power to take one's life, other than for murder. The state execution of murderers is required because a murderer has taken the life of another human being made in God's image. In a Christian worldview God has ultimately decided what is moral or immoral as revealed in Scripture. The Christian source for final authority rests in God and his revelation. He has created human beings and is therefore authorized to prescribe to us what the rules in life will be.
Governments without a check on their power to take innocent life wind up becoming tyrannical. They create laws that benefits those in power and often persecute those who have no power. This is just one major difference between these two worldviews and how they work themselves out in real life. Ideas have consequences. History has shown that without the moderating influence of the Christian faith within a culture, the government becomes the final authority for morality in which there are no protected rights for the individual.