Just one other thought on this.
IMHO I don't believe that governments should be involved in who can marry in the first place. The government should only be concerned about who can form an economic unit under the law for purposes of taxation, inheritance etc. If any couple be they heterosexual or homosexual want to form an economic union they should legally be allowed to do so with the privileges and responsibilities that go along with it.
The way it is now it discriminates against two siblings who might want to co-habitate and combine their financial resources. Why shouldn't a a parent and adult child be able to form an economic union under the law.
As it stands right now any non-related couple can marry thus forming an economic union whether they are actually consummating the relationship or not. Is anyone really going to check?
He has told you, O man, what is good ; And what does the LORD require of you But to do justice, to love kindness, And to walk humbly with your God.
Micah 6:8