Stalin, Polpot and others didn't go to war because they were atheists, they did it because they were dicks.
This counter point seems to always come up by religionists to try and defame atheism.
The reality is these people were solely endeavored to obtain complete control of the population centering the power unto themselves without any
crippling diversion from anyone or any established organization, either by political or religious expression.
Centering the power directly at themselves but propagandized to the masses that it was better this way for the greater population.
And they used their acquired control by using military force to achieve this goal, killing millions in the process..
This is by no means an expression of modern secular humanism by any tangible understanding.