The next topic I would like to summarize from Discussing Marriage is the argument from Libertarianism.  This may seem like a strange argument at this point, but hopefully we can see some merits in the response.  I would summarize the argument thus:

P1:  Legal marriage of any kind is beyond the scope of government
P2:  Marriage is more appropriately part of a religious observance
C1:  Government should get out of the marriage business altogether

I can see how this would appeal to libertarians.  The response involves whether or not legal traditional marriage promotes the general welfare sufficiently for the government to be involved.  Legal marriage is an important type of contract where husband and wife agree to take responsibility for the children they have as the result of a conjugal marriage.  Without some level of legal contract, a provider could simply decide to leave their dependent spouse and children with no legal consequences.  Thus, a significant reason why government is involved in marriage in the first place is to protect the well being of a dependent spouse and/or children in a traditional marriage.

Once again, this comes back to the crucial distinction of a conjugal view of marriage.  And this argument provides another insight to the rationale behind defining marriage in a traditional way.