I think we already have contract marriage. People marry for money all the time, otherwise Donald Trump and that rodent living on his head would be single. All one needs are two consenting adults. Incest? That is another issue, but if both parties are consenting and of legal age, what business is it of yours?<quoted text>At least s.v.o.h. agrees, the arguments for same sex marriage support polygamy too. Marriage equality means same sex marriage and polygamy too. Not long until incest marriage and contract marriage come along for the party.
It was common practice for sisters and brothers to marry in royalty to keep blood lines pure. No need for us commoners to spoil their lines with our inferior genes. Cleopatra VII and Ptolemy XII married after their father died and ruled Egypt. You do like tradition, don't you?