Copernicus
Industrial Strength Linguist
Not at all the facts of history are clear: Theism in and of the nature of the beliefs do not cause immorality. The tribal nature and the nature of humanity determines the morals/immorality, and this is not only not caused by Theism, but morals are are natural outcomes over timem and variable and subjective over time and a poor measure of any generalization of what causes immorality.
Very bad wording of your argument against Theism based an unfortunate atheist/agnostic agenda. Theism is not the scapegoat for human immorality. Ancient Religions essentially fail to provide an adequate contemporary standard of morality that deals woth the diversity of evolving human cultures.
I agree with you about where moral and immoral behavior come from--the examples set by role models and peers. However, those same sources can teach reliance on religious doctrine, which can preach violence against people considered to deviate from the dogma. People who rely on authoritarian dogma may be predisposed to justify bad behavior, if they are convinced that a "higher power" ordains, excuses, and/or exonerates it. Those terrorists who crashed airliners into buildings considered themselves to be devout instruments of their God's will, even if most Muslims did not and rejected their behavior as evil. People who murder abortion doctors and blow up clinics can also do so in the belief that they are fulfilling a Christian God's will. It's not that religious morality predisposes people to violence, but it can often be a catalyst that magnifies a predisposition to commit violence.