Hey, when we're wrong, we can admit it.
So, it turns out that for about a year (in 1793-1794), in France, there did exist a group called "The Cult of Reason" and not only were these people explicitly atheists, but they also did some nasty things (including joining in the general anti-clericism going on at that time, killing priests and descrating churches) in the name of Atheism.
For further information:
No excuses. They did it. It was wrong.