I see theists referring to people like Stalin, Lenin, Polpot and Mau-mau as having killed thousands or even millions of people in the name of atheism. Then they ask the same old question. How can you defend those atheist for their crimes? Wouldn't they have been better off with the calming hand of God on their hearts? These and others like them are at best a poor argument for a God. They prove nothing, and really have nothing to do with whether atheism in itself is inherently good or bad. There are several reasons that this is true.
the most compelling argument for me is this. All the cases mentioned above, the motivation of eliminating religion had much more to do with consolidation of power into the hands of a dictatorial government than it ever did with atheism itself. The church, any church or religion, is a threat to that consolidation of power, therefore it has to be done away with.
In a dictatorship,or really any type of government where power is held by a very small group of people, there either has to be no religion, or the government must be a theocracy in and of itself. There may be some slight tolerance for other religions in a theocracy, but the laws of the land so to speak are laid down by the ruling theology.
Stalin, Lenin, Polpot and Mau-mau are examples of governments or dictators who felt religion was not needed to control the people, where violence could do as good a job by itself. Governments like those in Iran, Saudi Arabia, Syria and the government people like Rick Santorum and Sarah Palin would like to see the U.S. become, are examples of governments which prefer religious oppression and violence to control the people.
In a very few cases, the government is truly trying to make things better for their people, but in most cases, both scenarios above are primarily a method of control of the masses. In some extreme cases such as North Korea, you have a dictator who considers himself to not only be the leader of his people, but literally the god of his people entitled to the same worship and praise as any "God".
Therefore to claim that atheism was a driving force to any of these people is a nonstarter. Atheism was at best a byproduct of removing the threat to power. So yes there have been atheist who have killed many many people, but they did not kill in the name of atheism, but in the name of power. I personally cannot condone the actions of these people, but I also can't see how it has anything to do with why I or anyone should believe in a god.