I think not including Atheism or what we can say in other words Communism or Communist Ideology or Secularism, whatever, in Civilization 4, is a mistake on the part of the developers which they will definitely realize later. Like all the religions/philosophies, this "ISM" had a great influence on the human race. It is part of the history, just remember the Soviet Union as well as even today many people in East Asia have no religion. With Darwin's theory at the beginning of the industrial revolution this "ISM" had a very strong influence in the West and thereafter throughout the World. People moved much much away from their religions and thought that humans can themselves achieve everything with their own efforts through scientific progress and make the world a paradise. They began to call "God is dead"! This inspiration gave them much confidence in this "ISM" and they did really make many achievements. This idea spread like wildfire at that time throughout the world and people began to consider older religions as superstitions. So this religion/philosophy/ideology or whatever you call it deserves to be included in Civilization 4 and I think the developers should include this now or address this mistake in a patch after the release of the game. I hope this will happen.