People believe what it suits them to believe - evidence doesn't come into it - they will search for the tiniest scrap of evidence that supports that belief and desperately hang onto it.
Like people who don't believe in man made global warming despite every single scientific society in the world backing it, they'll still find some disgruntled retired physicist and hang onto his every word.
People generally don't make decisions based on facts and evidence
How many people buy cars based on checklists of features? that might start the process but in the end its about getting people to imagine themselves behind the wheel feeling good.
Same with conspiracy theories - people get a buzz about feeling that they're smarter than all the "experts".
Not read it but I hear this book's quite interesting
http://www.nytimes.co...ong-the-truthers.html
About the "Truthers", who think 9/11 was a conspiracy, not looking at the conspiracy but about the people and their culture, what they get out of it