The book does not teach anything. It posits a historical alternative.
Jeez, we're all prickly today, aren't we?
I have read
Holy Blood, Holy Grail and found it both fascinating and informative. The whole history of Rennes-le-Chateau, Knights Templar, and the
Sang real made for quite titillating reading. The authors made an interesting and original argument for their hypothesis.
Oh yeah, and I didn't lose my faith, either. Try reading The Vicars of Christ sometime... now that book will shake yer faith but good.