Forgot where I heard it from, an interview with Dawkins I think...
"If one person suffers a delusion, it's called insanity,
If many people suffer a delusion, it's called religion."
'When one person suffers from a delusion, it is called insanity. When many people suffer from a delusion it is called Religion.' - Robert M. Pirsig, author of Zen and the Art of Motorcycle Maintenance
Richard Dawkins referred to this quote on his book, The Gawd Delusion.