Some people believe in an invisible man who impregnated a human female and they gets lots of power and money for preaching about it. Who's to say if that's a mass delusion? There's lots of alien microbes on earth.....what's to say those microbes from passing Astroroids and meteorites didn't jump start life here? Just because your beliefs are not popular doesn't nessasarly make it a delusion. So far humans are not capable of proving or disproving such things.