It is clear from reactions to the Supreme Court rulings on same-sex marriage that many Americans do not understand the public purpose of marriage.
Marriage has a public and a private purpose. The public purpose of marriage is to unite men to women and both to any children they produce. Governments recognize marriage because it is an institution that benefits society and children like no other relationship. Where marriage declines, government grows, intrudes, and steps in to pick up the pieces.
Read more at http://www.afain.net/Changing_Marriage.pdf