I have a couple thoughts on the whole marriage issue and civil union debate. I think there are fundamental questions that need to be addressed or determined. I put my disclaimer on this for lack of time to fully research or document, it's just a thought.
Origin of Marriage (religion or government?)
The Biblical picture would indicate that marriage is a religious institution or origin. Marriage is a religious union between man and woman as ordained and joined by God. (see Mark 10:7-9), also referring back to Genesis where God made them male and female in his image. This also refers to the married couple becoming ONE. This also points a bit to Ephesians 5 where it compares (maybe equivalent) husband and wife to Jesus and church.
In some quick searches on the Internet (google/wikipedia/others) most attribute the origin of marriage to human invention and politely pass off or ignore the "recorded history" of the Bible in Genesis indicating prior institution than what they indicate by 'man'.
If this is truly the case (that marriage origin is religious, and not a human/civil invention) then I would get the picture that God originated marriage, then humans (civil government) recognized the value chose to encourage it through civil recognition, and granting additional civil rights and benefits.
Who has the right to re-define marriage?
If that is the picture, then civil government, really has no right to re-define a religious institution, such as marriage. The church really has no right to re-define it either, since it was clearly instituted by God (not religious leaders such as Pharisees, Elders, Apostles, etc...) They do not own it, but must either define their own, or try to hijack this wonderful religious institution.
There are all sorts of implications and options that one could take from verifying and understanding this. If you have thoughts about what this would mean (positive or negative implications), please comment.