Us atheists have had to put up with a lot of manure being pedalled as informed ethics in order to smear us with the crimes of Pol Pot, Stalin and Hitler. We got it from hardcore apologists, we get it from culture warriors, most of all though, we get it from fakes. Bigoted phobics who want to maintain the "moral instruction" of their flock through fraudulent pretence to moral authority.
They say that their morality comes from God, which in turn through their scholarship of their religions texts, naturally puts them in a position of power relative to their flock. The idea that the Godless can discern morality threatens these snake-oil moralists, these theological demagogues who never adapted to the Enlightenment.
Take the hypothetical story of Bruce babysitting little Timmy...
Bruce was born Godless into a non-God-fearing family who never went to church nor had a Bible in their house. His parent's parents weren't church goers either and Bruce's Grandparents kept their religious views to themselves. Suffice to say, Bruce doesn't even know of a single baptism in his family, although he suspects some of the extended family may have...
Bruce faked being a Christian (to male and adult Christians) when he was a teenager. But that was to pick up Christian girls... He regrets the deception, but nothing else.
Bruce's exposure to the Bible came later in life, and of what good Bruce found in the bible, he had already discovered by working out how to treat other people well. His exposure to other religions later in life were the same. Bruce's morality doesn't stem from religious culture.
Bruce is babysitting little Timmy. Timmy is being a pest and for some (Warner Bros. motivated) reason, the idea of dropping an ACME anvil (or analogue) on Timmy's head comes to mind. Automatically, Bruce recognises that immoral acts by definition are those that cause the most harm and rights of the idea of dropping heavy things on little Timmy as being immoral.
Bruce discerns the moral course of action and God and his followers are nowhere to be found. Bruce makes far less comical moral decisions all the time and apparently God isn't a part of those transactions, much less the Church.
There is no evidence that morality stems from God before even considering God's existence. There is no evidence that the apologists and culture warriors have a divine mandate.
The line of argument from the apologists has been that if one abandons God, then one abandons morality; which is quite clearly a load of crap. Conversely, if one abandons reason, one can find a way to justify anything.
I'll stick with reason thanks.
So how do the apologists maintain their Godless = NAZIism, Stalinism, etcism line without this claim. The negative claim (no morals) won't work so they are left only with positive claims; that atheism actively promotes immoral acts rather than simple removes one's inhibitions.
So how are they going to support this claim? What evidence will they use?
Hitler didn't kill people because atheism told him to kill people. He killed people because he wanted to. He wasn't fussy about who he recruited either; positive Christianity people... Of course, this was just lip service to Christianity and there was nothing in Christianity to mandate the killing. Just like there was nothing in atheism to mandate it.
The deal between Russian Communism and atheism; same deal. Lip service. Atheism was promoted at the same time as a lot of killing, but atheism didn't lead to the killing. Sure, atheism was promoted the wrong way and there was coercion, but if we start saying that coercion into X means that X leads to coercion is stupid.
That's as stupid as saying that sex has been coerced by some people, ergo all sex leads to coercion. Rubbish.
The simple fact is, the apologists and culture warriors have never put forward a factually sound positive motivation for violence as afforded by atheism. That's understandable, given that we don't have monolithic churches pontificating, bibles to thump nor a God to pray to.
Atheism doesn't mandate a whole lot. Atheism is about a truth state concerning the existence of God. Attempts to make it into something else are doomed to failure and persistent attempts demonstrate only the demagogue's lack of respect for honesty.
So negative claim is easily debunked and a reliable positive claim is yet to be forthcoming. How can people make the claim that atheism leads to immorality with out the valid supporting premises / evidence?
It's called lying and it's motivated at least by bigotry and quite possibly through a thirst for power.