The Priory of Sion, a 1950's hoax, is not a real organization. Dan Brown's description of Westminster Abbey, as one example, is riddled with errors, as NT Wright describes here:
http://www.spu.edu/depts/uc/response/summer2k5/features/davincicode.asp
And in what you printed, Dan Brown admits that he believes the theories he puts in his book, despite their lack of any factual evidence, and obviously he wants his readers to believe them as well, and uses objectively false statements of history to try and accomplish this. His descriptions of history, as with the Council of Nicaea and Sir Isaac Newton, are objectively false as have been shown by many.
I believe alot of things to be true that may or may not stand the test of time. The problem is you apparently
think others are too stupid to think for themselves.