Where is atheism more prevalent historically, in rising culture or in decaying cultures?
What does that have to do with anything? The vast majority of atheists hold the same moral view as religionists. They just replace gods with the state. The state is their god. Both religionists and leftists, which the vast, vast majority of atheists are, are totalitarian authoritarians. Leftists have their gulags, Religionists their inquisition. They're just two sides of the same coin.
Compare Hitler or stalin to religionists in terms of basic ideas:
In metaphysics: Unreality. The Nazis preached polylogism which means that they affirmed the primacy of consciousness. Religions affirm the primacy of consciousness as their starting point.
In epistemology: Both the Nazis and stalin were anti-reason. They both preached faith. Have faith in the plan. Have faith in the volk. Don't dare rely on your own thinking. Listen to your leaders and obey. They were polylogists which means they affirmed the primacy of consciousness. Reality is different for the jews then it is for the arian. Religions also preach faith and the subordination of the mind to authority. For the Nazis and the communists, it was the state, the people, or the collective. For religionists it's gods. For Plato, it was the supernatural world of forms. It's all the same idea, just different packaging. Religion of course explicitly affirms the primacy of consciousness. What is faith? Faith is wishful thinking. It says so right in the bible. Faith is the supstance of that which is hoped for. What is the substance of hope but a wish?
In ethics: Self-sacrifice as a virtue. The Nazis and the communists preached self-sacrifice to the state. They preached that the individual must set aside his own plans and goals and desires for the desires of the state or the people or the collective. Religionist preach self-sacrifice as a virtue and not just self=sacrifice but the sacrifice of the good to the evil, the ideal for the non-ideal. Where do you think the whole notion of progressive taxation comes from?
In politics: Collectivism, which is the political expression of the morality of self-sacrifice. In religion the individual serves god. In Naziism and Communism, the individual serves the collective. Both hold individuals as sacrificial animals.
There is no difference between the two, religion and most atheists, in terms of fundamental ideas. Always look to the fundamental ideas of any society.
Contrast both with Objectivism:
In metaphysics: Objecive reality. There is only one reality and everything is what it is and does what it does independent of conscious intentions. The primacy of existence.
In epistemology: Reason. Reason is the faculty of individuals which perceives identifies and integrates the things in reality. It doesn't create them. It is man's only means of knowledge and man's basic means of survival. Consequently, faith has no place in human life. Faith is not a reliable means of obtaining knowledge of reality.
In ethics: Rational self-interest. The rational part is kind of redundant since it is never in anyone's interest to act irrationally. Sacrifice of any kind is evil.
In politics: Capitalism. Complete, uncompromised free trade. An absolute separtation between the state and economics. Individualism. The recognition of individual rights as an absolute, not to be infringed.