Religiosity goes FAR deeper than Bible thumping. It seems to be an extremely common aberration in human cognition (which suggests it was evolutionary advantageous).
Have you ever tried talking a hippie out of her "I need these crystals to cleanse my body of toxins" style of faith? It is just as impossible as trying to reason with the hardcorist of fundamentalist Christians.
I call this the milk rule. I don't think it's about rational arguments not working, I think it's about not starting out by putting the person on the defensive. The reason I call it the milk rule is because it's something I learned when I was in fifth grade. I didn't drink milk. Many people thought I should. I told them milk wasn't really all that healthy. They told me that it was just about the healthiest thing ever. We didn't agree. I eventually realized that they felt so strongly about milk because from an early age their parents told them to drink their milk because they needed it to grow strong. By telling them it wasn't really all that healthy I was not making an argument against milk as far as they were concerned, I was calling their parents liars. Once you draw that line in the sand people will not be swayed. I learned to not call people's parents liars when I was trying to persuade them.