Tally up the democide death toll from secular nations in the 20th century alone and then compare that to the previous 2000 years of religious killings and you might change your tune.
Every indication is that secular nations cannot remain free. At some level, God must play a part or it is unhinged from moral strictures. The US did not start out a purely secular nation; that is only the last 50 years and the more secular we become the closer we get to the killing fields.
This is false. Ideologies cause conflict. Religions account for most of them. We've had our share of idealogues not directly influenced by religion who have been trouble makers too. Humans are capable of ruthless and cruel ambition no matter what their world view is. I would say the capacity to commit atrocities is a human trait.
We have to realize Stalin and Hitler were in a time when the Earth was much more populated than many previous times of war, and the advancement in weapon technology had advance to a point where bombs and machine guns allowed for immensely larger scale bloodshed. The population of the Earth was up to around 450 million by 1340 C.E. but after the great famine and the Black Death in 1350 C.E. the population dropped drastically. In 1500 C.E., there were only about a total of 370 million people on Earth. The population shortly began to balloon because humans had re-learned agricultural methods, irrigation and governments were re-established. 314 million is about what the United States has today alone. Until the 11th millennium B.C.E. the population is estimated to have topped out at 3 million people. During the time of Hitler and Stalin the Earth’s population had popped up to around (2 billion) and weaponry technology allowed for the subjugation and the genocide of people by the millions, instead of hundreds of thousands. Using a higher number to substantiate someone as bigger villain is improper logic. Had the perpetrators of the crusades had machine guns and Jets dropping bombs on a larger population, you can guarantee there would have been higher death tolls.
Over Millennium humans have coordinated slaughter on millions of other humans for territorial claims, religion and nationalism. Dictators with no religious affiliation are not simply killing for Atheism, they are killing for power. Religions have historically had power and dictators are often not looking to compete with alternative potential threats which may have influence or gain power. Stalin was killing for Marxism and totalitarian rule.
It’s true that the tyrannical communist regimes of Mao and Stalin were opposed to religion, with religious belief discouraged and punished under their rule. This had less to do with atheism and more to do with the threat of religion as competition with their own tyrannical plans. Totalitarian regimes are built on dogma and fear, not freedom of speech and inquiry. In this way, they greatly resemble religion. In effect, these leaders essentially created religions and inserted themselves at the top as new deities. As Sam Harris put it, “The problem with fascism and communism, however, is not that they are too critical of religion; the problem is that they are too much like religions.”
Maybe around the time of the communist revolution in China, roughly 30 millions died for some reasons, including starvation, illnesses, warfare and senility. That’s only about 5% of the population back then.
In Europe, the Catholic church ordered people to massively kill cats, and as a result, mice increased in number, spread plague all over Western Europe and killed over 30% of the population back then. But Europeans have never seemed to blame the church and its popes…
https://skeptoid.com/episodes/4076