Right. Communism.
Atheism has as little to do with Communism as you claim that real Christianity has to do with genocide.
And it’s not atheists who have a holy book which provides examples of righteous and justifiable genocidal activities, including the mass slaughter of babies and children and the mass enslavement and rape of virgin women.
Remember, God supposedly commanded these things, and thus according to Christianity genocide, rape, and enslavement are sometimes a “good thing”.
Can you provide examples of where Christianity said that?
It has plenty to do with Communism. Communism is the political result when man's God-given rights are deemed to be non-existent and are subordinated to the greater good of the "collective".
Not all atheists are communists but all true communists are atheists. Communism is just one of the false directions in which atheism leads so not all atheists end up as communists but many do. All communist countries were officially atheist and persecuted religion and its believers. For good reason. It is enshrined in the writings of communism's founder.
Read Marx, the originator of the communist lie. One of the cornerstones on which his writings were built was that the proletariat was oppressed by religion and needed to be "liberated" from it. Millions lost their lives as a result. The construction of the workers' utopia was the cause which caused these millions to be sacrificed. For a materialist, godless paradise in the here and now which turned into a living hell.
Minor point. True atheism is not common. Many people who claim not to believe in God are simply agnostics and many angry agnostics are often mistaken for atheists. They're people who won't believe because they're not satisfied with the arguments for the existence of God and angrily demand proof. Atheism on the other hand, is a positive believe in the non-existence of God. A "faith" if you will, that God does not exist. Just as Christians have a positive belief in the existence of God, the atheist believes in His non-existence. Like any faith, it tends towards evangelism and militancy among its followers. Hence the drive of its followers to spread it throughout the world.