Maybe it's all about prestige, being part of the "club"...I can't imagine intelligent people believing this. These are the same people who can't believe in Jesus? That's too far fetched? That's easy math compaired to believing we all have an alien living in our brains: Thetan is a " non-human, but not superhuman, parasitic intelligence that can infest the brains of human beings".
WOOOHHOOOOO, these headaches must be that pseky Thetan trying to get out (like on the Alien movie)