Add up the deaths that were attributed to Hitler, Stalin and Pot. Then round up for good measure. You can safely say that the number is staggering. Probably upwards of fifteen million. However, consider the following conflicts where the only differences between the opposing factions were and are religion:
Albigensian Crusade, 1208-49
Algeria, 1992-
Baha'is, 1848-54
Bosnia, 1992-95
Boxer Rebellion, 1899-1901
Christian Romans, 30-313 CE
Croatia, 1991-92
English Civil War, 1642-46
Holocaust, 1938-45
Huguenot Wars, 1562-1598
India, 1992-2002
India: Suttee & Thugs
Indo-Pakistani Partition, 1947
Iran, Islamic Republic, 1979-
Iraq, Shiites, 1991-92
Jews, 1348
Jonestown, 1978
Lebanon 1860 / 1975-92
Molucca Is., 1999-
Mongolia, 1937-39
Northern Ireland, 1974-98
Russian pogroms 1905-06 / 1917-22
St. Bartholemew Massacre, 1572
Shang China, ca. 1300-1050 BCE
Shimabara Revolt, Japan 1637-38
Sikh uprising, India, 1984-91
Spanish Inquisition, 1478-1834
Taiping Rebellion, 1850-64
Thirty Years War, 1618-48
Tudor England
Vietnam, 1800s
Witch Hunts, 1400-1800
Xhosa, 1857
Arab Outbreak, 7th Century CE
Arab-Israeli Wars, 1948-
Al Qaeda, 1993-
Crusades, 1095-1291
Dutch Revolt, 1566-1609
Nigeria, 1990s, 2000s
If you add up all of the lives that were lost in the name of one religion or another, you come up with a staggering figure that is in excess of eight-hundred-million. That's eight-hundred-million. An eight, followed by eight zeros. So, even if the believers who are uneducated enough to think that Hitler, Stalin and Pot were psychotic mass murderers because they thought these men were atheists, it is horrifically clear that religious murder wins out.