the problem with communist regimes was not the ban of religion but the elevation of nationalism to a substitute religion. in the chinese communism, for example, mao was worshiped like jesus which made it impossible to question his decissions in public due to the wrath of the believers. even after he died the party could tell the people everything and claim that it would've been maos will.

atheism without substitue is an utopia because many people are not capable to live with the complexity of the world and need easy answeres. some people can only not kill if they can lable killing with "evil". but i think an atheistic society would just not have a lot of problems we have right now. and if there are social problems that have to be discussed, at least everybody has to come up with convincing arguments and can not claim his interpretation of magic book as the will of magic man that has to be followed for magic reasons.