The problem with religious belief, as Sam Harris has observed at length in "The End of Faith", is not so much belief in God as belief upon bad evidence in anything. Did Stalin and Hitler champion free debate? Or did they command, as does the Old Testament:

"If your brother, the son of your father or of your mother, or your son or daughter, or the spouse whom you embrace, or your most intimate friend, tries to secretly seduce you, saying, "Let us go and serve other gods," unknown to you or your ancestors before you, gods of the peoples surrounding you, whether near you or far away, anywhere throughout the world, you must not consent, you must not listen to him; you must show him no pity, you must not spare him or conceal his guilt. No, you must kill him, your hand must strike the first blow in putting him to death and the hands of the rest of the people following. You must stone him to death, since he has tried to divert you from Yahweh your God." (Deuteronomy 13:7-11)

This was also the rule which Stalin set for Communism, and Hitler for Nazism: if your brother tries to tell you why Marx is wrong, or why Jews are not actually plotting to take over the world, then do not debate him or try to set forth your evidence, do not perform replicable experiments or examine history, but turn him in at once to the secret police.

It is not God, but belief upon insufficient or distorted or unreasonable evidence; it is not God, but the imposition of beliefs by force rather than reasoned argument; it is not just God that is the problem. Which is a more damning condemnation of all religions and Communism and Nazism, as special cases of this one unifying rule, than anything you could say about one particular God.

For the argument that violence follows empirically upon bad rationality (that from socially systematized belief in insane things upon bad evidence, will nearly inevitably follow imposition of beliefs by force) I refer you to Sam Harris's The End of Faith.