I'm saying there is no difference between the two, except that a handful of atheists have racheted up a tremendous casualty list.
The largest casualty list in history (normalized to the population of the region reachable by available transportation technology) was compiled by Genghis Khan. He is presumed to have been born and raised as a shamanist, a faith that neither you monotheists nor we atheists have to claim as one of ours. Once he completed his bloody rise to power, he may have become interested in Buddhism and the Dao, just as we all adopt a nicer philosophy once we are done with the vile acts of our youth.
With that out of the way I continue to object to the way you measure evil, and to glibly insist that there is no important difference between the one-god faction and the zero-god faction except for the debatable thesis that atheism is responsible for a larger mountain of human corpses.
Even accepting that thesis for the sake of the argument, we must still face the fact that all human lives are ultimately finite and that sooner or later almost every one of us will be unmourned. The whole point of civilization is that it is an organism unto itself that transcends the lives of the mortals who build and maintain it. The immortality we seek is not in some imaginary afterlife, but in our civilization. Civilization is qualitatively more important and more valuable than we are.
Civilizations are rare and irreplaceable. To destroy a civilization is qualitatively worse than murdering almost any number of people. To destroy three civilizations--half of the six we managed to create--as the Children of Abraham have done, is the greatest evil that has ever been performed.
I cannot hold every individual Abrahamist responsible for this, since most people of any stripe are not that familiar with world history. But I can and will forever hold it up as the ultimate rejection of any educated Abrahamist with the temerity to argue that his religion has, on the balance, been a force for good in the world. The evil of Abrahamism is, at least so far, unmatchable.