In some books, I'm thinking of Dresden Files, I think it has less to do with the faith of the vampire and more to do with the faith of the person using the symbol. With Dresden, he uses a silver pentacle that his mother gave him and it has the same effect.
Because it makes his job harder. He hates having to work for his money. He just wants customers to put money directly in his bank account without ever having to work for it. Other storefronts? Cheating him out of sales. Other payment systems? Stealing his money. Other operating systems? Making his life hard by forcing him to accommodate for something different.
There is still an issue of human bias, though. A thought is not accepted unless it's widely accepted. Even much of our established science was once a pipe dream, even with reproducible proof, until it was accepted on a wider scale.
It's not as simple as just providing proof and letting people accept it, you have to appeal to them. Which is exactly what politicians do.