Sorry for the rant. I lost control as I was writing.
It's alright. I don't purely blame atheism for the 100 million deaths I mentioned. I was trying to prove a point.
People frequently blame religious belief for wars between religions, When religious groups fight, what is really happening is conflict between people with opposing worldviews. One group says the world is one way, and one says its the other. And almost 100% of the time, including even the most purely religious wars like the Crusades, the real motives for the fighting are economic and political. Someone is trying to line their pockets or gain territory and power, and its framed as a "War for God," just like the current U.S. wars are framed as wars for Freedom.
Atheism is not a religion, but it is a worldview just like Christianity or Islam. The one belief an atheist must have to be an atheist is that all religions are false. Therefore, religious people are wrong. They are either brainwashed, less intelligent, or innocently misled by tradition. But either way, they are the opponents of public education about the true, godless nature of the universe - they are the outgroup. They represent outdated, ancient, and oppressive modes of thought, while atheism represents the modern, progressive, intelligent, and rational in society.
In large part (this is a generalization) Atheism regards religious people as the brainwashed. The people mainlining the opiate of the masses. And the brainwashed don't know what's good for them, so in the last century, atheists felt morally justified in outlawing religion when they came to power, and killing or oppressing the religious. Which they did. In Spain, Russia, Cambodia, China, and the list goes on.
So while it's true that Atheism has no holy books, or sacred laws, what is has is a shared worldview. And when people with this worldview come into contact with people who have another worldview, there is fighting, violence, repression, and death. Atheism has proved no different from any religion in this regard.
That was my point, in so many words.