When South Florida atheists held their first meeting, they were just five friends, having a beer at a bar. Four years later, they've moved to a bigger place -- still a bar -- to hold their weekly meet-and-greets. Membership is up to almost 500, Darwin Day is in the planning stages and bumper stickers are on sale. "There is no God, but ice-cream is great," reads one. "What schools need is a moment of science," reads another. Atheist groups are growing all over the United States, challenging stereotypes and confronting what they consider a big backslide in the separation of...