Modern science has debunked the myth that there are significant health problems with close relatives procreating. First cousins may marry in many states, why not siblings?<quoted text>
...Just as there are scientific studies providing justification for outlawing marriage between close relatives, there are plenty of sociological studies detailing the harmful effects of polygamous marriages, besides the legal issues concerning inheritance, property distribution etc
And procreation is irrelevant to marriage, right? So why can't I marry my brother?