I was considering this issue from another point of view.

If a 30 year old man walked into the County Clerk's Office and applied for a marriage license. The other adult consenting party was the man's 28 year old sister. Would this be an issue?

If a 65 year old consenting woman walked into the County Clerk's Office and applied for a marriage license. The other consenting adult party was the woman's 35 year old son. Would this be an issue?

What boundaries, if any, does your local political jurisdiction place upon the two parties who wish to enter into a legally binding marriage?

Why does a court marriage only have to be between two consenting adults? Why not six consenting adults?

IMO, this is a legal issue and therefore a political issue. If no one cared, then the law would be changed, as it has been in several jurisdictions. The interesting part of the reinterpretation of the laws regarding marriage is how the courts have taken a leading role in redefining what marriage is and what types of parties can enter into this contract. I think this leading role by the courts is what causes so many people to associate the civil rights movement of the 1950's and 1960's with the same sex marriage movement of today.