In a prison cell interview before he died, Jeffrey Dahmer, the homicidal cannibal, when asked why he did his terrible deeds, said that when he came to believe that there was no God and that we had evolved from slime, and that he felt there was no moral restraints that should hold him back.
People do things for complex personal reasons, and then search for justifications.
It is more likely that Dahmer's impulse was his drive for personal dominance and lack of consideration for his victims, and he rationalized after the fact that evolution and atheism made it all right. Most evolutionists and atheists live virtuous lives. One finds few, if any, atheists in prison. David Koresh and Charles Manson found in the Bible justification for what they did. Or would it prove, as I said about evolution and atheism, that people choose what to do and then find whatever justification they can think of as excuses.