Stalinist Russia and Maoist China are good examples (of atheism’s evil consequences).
I agree with you that atheists have committed terrible crimes, but so have religious people. The Crusades, pogroms, the Inquisition, the religious wars of the sixteenth and seventeenth centuries are examples of horrific crimes against humanity committed by religious people.
I do not believe that atheism in itself makes one more moral than a religious person. Atheism only addresses the issue: Is there a God? It does not address how we should interact with our fellow human beings. The scientific method does not address this issue either. That is where Secular Humanism comes in.
I believe that it is true that Humanism may well draw many principles from the teachings of Jesus, but the teachings of Jesus (turn the other cheek) and the teachings of Humanism are in direct opposition to the teachings of the first half of the Bible (an eye for an eye). Unfortunately the early Church abandoned Jesus’ compassion for OT law and judgmentalism. I believe that it this deviation from the teachings of Jesus that has been the root cause of the crimes committed in the name of Christianity.
I believe that the teachings of Jesus and of Buddha were a stepping stone from the brutality of the preceding millennia to modern day Humanism. So, yes, Humanism has Jesus to thank for many of its concepts, but to say that these concepts come from Christianity, in my opinion, is false. It was the Renaissance and the Enlightenment (the revival of Greek and Roman philosophy and art) and Secularism that slowly influenced Christianity to become less rigid, austere, and brutal and to behave in a more compassionate, Jesus-like manner.