Surely you've encountered the argument that atheism is the cause of so many deaths, via Stalin, Mao, etc.
When pressed to backup that claim, outside of a simply Association Fallacy, their response is typically along the lines of "atheism doesn't pressure/advise people not to be murderers, unlike believing in a god."
I've always thought this was silly. Here's a potential way of addressing it, that I'll throw out there.
A person, who is about to go and murder someone later in the evening, decides to prepare a nice dinner, using a recipe from a cook book. The cook book recipe does not persuade the person to not murder people... and thus the person goes and murders his/her victim.
Do we sue the cook book company for causing the murder? Maybe we take them to task for failing to prevent murder? Both would be silly, no?
The cause for the murder was whatever it was that pissed off the person, and the person's decision process to go do the deed. It makes as much sense to blame not believing in a sky wizard, that would be mad at you, if you murder someone, as it does to blame a cookbook that didn't persuade towards being peaceful instead.
We could blame an infinite amount of things that might have prevented the person from becoming a murderer, but they'd all get an equal share of the blame... which averages out to about zero.
Atheism does not cause anything. It does not prevent anything. Neither does being bald cause or prevent anything (other than having hair). It's nonsensical to blame being bald for causing murder.
While a belief in a god can confine our violent tendencies, that just means that without that belief, we'd need a substitute... something that humans do naturally 99.9% of the time, anyway - secular morality.