My family is Catholic. I told my mother I'm an atheist and now she says she has failed me as a mother. You think she'd say that if she wasn't religious? No. Religion can cause deep rifts. For example: 9/11, the crusades, Israel/Palestine issue, etc. I know many people who have been estranged from their families simply for having different beliefs-religion promotes intolerance. And I am sincerely hoping you don't mean a scientific theory when you say "theory".