Jokes on you, apparently in the Bible, God command marriages between first-cousin so you can't really blame on the religion on this one. More likely it's the society you can blame. Personnaly and even if i enjoy some incest mangas sometimes, i don't really think getting married with someone of my family is a good thing.It's just because the $insert-local-holy-book-title says that gay marriage or blood-related marriage are dirty.