Atheistic principles are not codified in a manner typical of theistic religion, but...
Many atheists claim a “lack of belief” in God, as opposed to an active disbelief in God. They claim to be accountable to the evidence and that, as they move through life, they are simply not confronted with any evidence that would compel them to conclude that he exists. Presumably, they make no positive truth claims and therefore believe themselves to be free from any burden of proof. The burden of proof, in their thinking, rests fully on the theist.
However, there can only be two possible explanations for the foundation of reality: personal forces or impersonal forces. Therefore, there are only two basic kinds of worldview: theistic and non-theistic. These basic categories are mutually exclusive and jointly exhaustive. Each person comes down on one side or the other, with no room for middle ground and no room for indecision.
Life itself necessitates a worldview. It is because of our worldview that we can relate with our world on more than just a physical, concrete level. Before we can interact socially and form moral or political values, we must first decide why we are here and, in light of that answer, how we should live. We may not have consciously arrived at all aspects of our worldview, but it is there—grounding and influencing all of our cognitive behaviors.
In other words, everyone has a worldview and no worldview is neutral. A so- called "lack of belief" in personal forces is in fact a positive claim that impersonal forces are the foundation of reality, which is—in effect—a positive claim that God is not the foundation. Regardless of what the atheist may claim, he has evaluated the evidence of the world around us and has made a call on the existence of God.
Furthermore, though atheistic principles are not codified in a manner typical of theistic religion, atheists are almost unanimous in elevating science as the ultimate authority. However, science as a study of the physical world lacks intrinsic authority and an absolute reference point whereby to inform societal values (as articulated in Hume’s “is-ought problem”). Thus, the “science” that is elevated by the atheist amounts to little more than the mainstream consensus of present-day scientists, making popular science the code to which the atheist will adhere. This renders the atheist particularly unstable in his prescriptions and allegiances because the mainstream consensus of scientists easily changes with the tide of public opinion and with the whims of corrupt dictators.