I happened to mention in my homily yesterday that atheists killed, according to some experts, in excess of 100 million people in China - this figure includes the Great Leap Forward.
After Mass a group of us discussed St Thomas' "Five Proofs", he ends each by saying, "... and this we may call God". For him God is the "Factor X" in the universe, though ultimately unknowable, it is knowable through reason, intuition and through revelation. It is benign intimately connected to mankind, for ultimately Factor X becomes Jesus Christ, Love made flesh.
An atheist Factor X is just the infill in the gaps in theories, and rather than being about wonder wonder or awe for atheist X = ignorance at best. The guiding principle behind the universe, if there is one, is either randomness or worse, competitive red in tooth and claw, Darwinian natural selection. Most atheists tend to see Man, both individually and collectively at war with the world around him, with his fellows. We see this in Marx's "class war", in Dawkins' "selfish gene", it is not benign, it is agressive, at its heart is "survival of the fittest.
It reduces love to chemical attraction, or self interest, there is a pessimissism here beyond anything Augustine could possibly put forward. More than that, death and destruction are its keynote, because man's survival depends ultimately on his conquering and destroying others, it is the embodiment of the "Culture of Death".
For Christians the guiding principle is "Life", atheism is about death. Therefore in the 20th century atheism lies behind Mao Zedung, Stalin, Hitler, Pol Pot. Atheists seem to be behind not just abortion but eugenics, family planning, radical feminism and the gay movement, political extremes of capitalism and communism and practically every evil I can think of.