Here’s my favorite definition for Atheism by Sam Harris:
No rational atheist (or “New Atheist”) holds religion accountable for every idiotic or unethical thing religious people do. We blame a religion only for what its adherents do as a direct result of its doctrines, such as opposing gay marriage or killing apostates.
Atheism has no doctrines. It does not demand that a person do anything, or refrain from doing anything, on the basis of his unbelief. Consequently, to know that someone is an atheist is to know almost nothing about him—apart from the fact that he does not accept the unwarranted claims of any religion.
Atheism is simply the condition of not believing in Poseidon, Thor, or any of the thousands of dead gods that lie in the graveyard we call mythology. To that extent, everyone knows exactly what it is to be an atheist—he has simply added the god of Abraham to the list of the dead.
If a belief in astrology were causing people to go berserk—to deny medical care to their children or to murder unbelievers—many of us would speak and write about the dangerous stupidity of astrology. This would not be bigotry or intolerance on our part. It would be a plea for basic human sanity. And that is all that an atheist’s criticism of religious tribalism and superstition ever is.
If you understand this, you will recognize any attempt to blame atheism for specific crimes, great or small, for what it is: A fresh act of religious demagoguery.