I myself don't try to discredit Darwin by blaming him for Hitler (mach shemo!) because the whole point of my argument is that in the absence of G-d there is nothing objectively morally wrong with genocide or selective breeding or hatred or mass murder or anything else. People who try to appeal to the non-theistically-based moral hang-ups of atheists are merely reinforcing the idea that some things are "obviously wrong" and "we don't need G-d" to tell us so.
Ain't I a consistent little thang???
"God" has historically been provided with a great many self-serving and arbitrary attributes, and has taken on many forms. He is a handy slate on which to write the conventions of morality. And consequently, "in the [presence] of God there is nothing objectively morally wrong with genocide or selective breeding or hatred or mass murder or anything else," so long as the person committing these morally reprehensible acts proclaims them to be the "will" of his God.
Which leaves us in a peculiar situation. If God is the source of morality, by what measure do we conclude that acts committed in the name of "God" are morally reprehensible?
You err.
There are plenty of biological reasons not to kill, steal, etc.
Very few animals kill their own, and when they do, it is under closely defined circumstances.