@Pastoralan, Communism in Russia was a belief system unto itself, it only promoted atheism as a means to replace it with a belief in the state (among illiterate peasants of Russia).
Yes it was anti-religious, and the state doctrine did worship Lenin (after he died and was put on display) and Stalin. But it used all the same tools as religion to control people.
Religion is not the same as faith; it has always been political (and still is in America). It is a means to tell people how to live their life. A moral policing - and if you get people to believe this is cheaper than paying for actual police. This isn't about God, this is about how people use religion to accumulate power. And Communist russia, or Maoist China used the same tools; just worshiping Lenin/Mao (and his little red book).
But i don't think you need to worry about your Fascism in Germany. There os a greater example of atrocities performed by Imperialist State Capitalism. The crimes of the British under Empire and US of A under manifest destiny. Compared to Communism, millions died of starvation and disease, in the USSR they accidentally caused a famine which killed millions in the name of their ideology (and they would have lied to cover it up, if they had felt the need, but you don't need to use propganda when violence will quell any opposition).
Under British rule they intentionally caused a famine in Ireland killing at least a million, the government exported food while the poor died, and the parliment decided that thinning the population would help the Irish escape the poverty they had perpetually suffered through (Capitalists tend to not give a shit about the poor, perhaps unlike Communists or Christians?). There was an element of rascism against the Irish going on aswell - and while the numbers may be smaller, 1 million out of a population of 8 is massive as a %, and they repeated this India on a much larger scale.
I don't know how you can breath the atrocities committed by Soviets and Nazis without remembering those committed by the British Empire, except that history is written by the winners. (It didn't end up helping the Irish escape poverty, instead it caused a downward economic spiral which saw the population drop - mostly emmigrating to the US and UK, for 120 years. Down from 8 million in 1840 to less than 3 million in 1960. People leave because there is no work, the reduction in demand means there is even less work and the spiral continues..). And this was for entirely economic reasons which their Capitalistic Empire was based on.
Look back to South Africa and you can see the British deploy concentration camps (think internment rather than death camp, there is some contention over the use of words here), the British invented the concentration camp (the Nazis merely perfected them?) in Australia the exported some aboriginals to island canps (where they were supposed to be educated into Christianity but instead died in massive numbers, often of depression and related illnesses, because that is what happens when you forcible destroy a culture and attempt to re-educate people - this is more leaning toward Imperialist attitude than economic ones, with a dash of religion thrown in for good measure).
And i will let you fill in the blanks yourself regarding the US of A, though untold deaths of slaves dumped into the sea to can be split the guilt between the British Empire ise of American colonies as cotton factories, the US's white masters exploitation of their workers pushing the demand for slaves, and the African slavers whose economy became based on warfare to capture slaves in order to sell for european weapons to wage war to capture more slaves... They all deserve a special place in Hell (if such a thing exists). Even if the British Empire eventually outlawed slavery (because free labour in the now independent US meant they couldn't compete, and because at the same time religious authorities in the UK became uncomfortable with enslaving Christian Africans, and you can really get things done when the Gods of Money and Abraham happen have aligned goals...). This lead to a destruction of the slaver states in Africa which relied on demand for slaves, it lead to slaver shops throwing their cargo into the sea rather than being captured by the British, and it had basically no effect on the US slave owners who could basically breed their own replacement slaves.
Still, it is not like the 20th Century was so much better, though many of the crimes of the British were taken over by the US after the second world war, as Pax Brittanica was replaced by Pax Americana.