Both think they are enlightened and blame things: the Bible, religion, atheism, communism. - Hiemere
The communism of Stalin was an irrational ideology in just the same way that all religions are irrational ideologies.
Check out the history of genetic research under Stalin for example. In 1948, genetics was officially declared "a bourgeois pseudoscience", more than 3,000 mainstream biologists were sent to prison, fired, or executed and scientific research in the field of genetics was effectively destroyed until the death of Stalin in 1953.
You are making a false comparison. When you can point to a dystopian society run on the principles of secular humanism, inspired by thinkers like Thomas Hobbes, Rene Descartes, Francis Bacon, Baruch Spinoza, David Hume etc then you will have a point.
Atheism is a necessary but not a sufficient condition of building a better world. It is an inevitable corollary of being rational.