Presuming that the principle of marriage (and certainly for relationships) presently being argued is that it is a recognised (sexual) union between consenting individuals could the society denies these same rights to other individuals who wish to contract marriage with multiple persons (polygamy or plyandriy) with close parents (incest) ? Examples abound to support this idea . http://www.time.com/time/video/player/0,32068,1754465091001_2120441,00.html?iid=tabvidrecirc http://www.guardian.co.uk/lifeandstyle/2002/jan/09/familyandrelationships.features103 http://news.bbc.co.uk/2/hi/europe/6424937.stm http://www.dailymail.co.uk/news/article-2356977/Iraqi-farmer-92-father-16-marries-second-time--woman-70-YEARS-younger-him.html http://www.brusselsjournal.com/node/301
Other cultures have polygamy and certain religious sects have in the past (and some still do today) practiced polygamy, so it wouldn't be a huge leap. The only thing that we would have make sure of is the express permission of all parties involved. We wouldn't want some guy marrying women all over the country without the other wives knowing about it. As for incest, that's an iffy one. For cousins and siblings, I don't see it as a big deal, but between parent and offspring, there is a huge potential for abuse similar to a boss and subordinate or teacher and student.
As far as Polygamy goes it's just recognizing and codifying something that has been practiced in the US for over a century. And legalizing incest is just recognizing the way of life of the Bible Belt.
