I would think that, at some point or other in our arcs toward or in atheism, a good number of us have seen the following quote:
Those who can make you believe absurdities can make you commit atrocities.
That quote was on my mind this morning, to the point where I Googled it and found via Wikiquote that it was part of a larger statement made by Voltaire. While the brief quote above is a powerful and disturbing statement, it is like many things taken out of a larger context in that it loses some of the impact from that context. Indeed, I find that the larger statement adds nuance and detail and even more power to what is already a potent assemblage of words.
That said, permit me to present the full text of Voltaire's statement, as it appears in Wikiquote:
Formerly there were those who said: You believe things that are incomprehensible, inconsistent, impossible because we have commanded you to believe them; go then and do what is unjust because we command it. Such people show admirable reasoning. Truly, whoever is able to make you absurd is able to make you unjust. If the God-given understanding of your mind does not resist a demand to believe what is impossible, then you will not resist a demand to do wrong to that God-given sense of justice in your heart. As soon as one faculty of your soul has been dominated, other faculties will follow as well. And from this derives all those crimes of religion which have overrun the world.