'Hi my name is Lindy and I deny the existence of the Holy Spirit and you should too.' With that five-second submission to YouTube, a 24-year-old who uses the name "menotsimple" has either condemned herself to an eternity of punishment in the afterlife or struck a courageous blow against superstition. She's one of more than 400 mostly young people who have joined a campaign by the Web site BlasphemyChallenge.com to stake their souls against the existence of God. That, of course, is the ultimate no-win wager, as the 17th-century French mathematician Blaise Pascal calculated—it can't be settled until you're dead,...