Atheism is the disbelief in the existence of any supernatural deity. This disbelief can take a number of forms, such as the assertion that deities do not exist, or the absence of any belief in any deity.
Stalin and Richard Dawkins are prominent atheists. Dawkins wrote a book, called "The God Delusion". Stalin is now dead, having killed millions of people in the name of Marxis-Leninism (which is predicated on atheism).
Since atheists have no God, as a philosophical framework atheism simply provides no logical basis for any moral standard. They live their lives according to the rule that "anything goes". In recent years, this has led to a large rise in crime, drug use, pre-marital sex, teenage pregnancy, pedophilia and bestiality.