My opinion .... Marriage should simply be a civil / government issued license between 2 consenting adults.

It's not that I disagree, but I wonder how we could - with a straight face - legally end discrimination against gay marriage and yet keep the ban on polygamy in place. Why just two people?

I think civil unions - a legal contract - should be open to anyone. 3 people, 5 people, cousins, a brother and sister, two brothers, anyone. When it comes to visitation rights in hospital, survivor benefits and the like, to deny anyone to designate whom they would like to receive these benefits would be bigotry in my opinion.

When the state gets involved with tax benefits, etc, however. you're looking at social engineering. Clearly society benefits when children are raised in stable families. Just as clearly, society is not helped by incestuous unions between brothers and sisters, therefore those are not to be so encouraged.

Gay marriages fall in the middle. I can easily see why the benefits of the social contract (again, hospital visitations, etc) should be allowed. I can't see the benefit of same-sex marriages to society, though, nor do I see why they are (from the point of view of society) superior to polygamous unions.