"The Law is an Ass." When there are nine lawyers, they make an Asinine.
"You can have your Christ and trees. You just have to realize that your religion is yours not to be forced down the throat of everyone else."
"I could care less your faith. You just can't legislate with it."
Nobody is trying to legislate one particular faith, or force it down anyone else's craw.
What almost all people in almost all times and places throughout recorded history have called "marriage," is the union of a man and a woman.
The "union" is the recognition by their society that they have societal rights and obligations toward each other, their kin, and their children if there be any.
My first anthropology prof mentioned that even in primitive societies, marriage exists to give societal status to the children as the offspring of both parents. Lineage can be of great importance to social status.
You can go back in ancient history as far back as there are written records, and farther: "These reconstructions push the origin of monogamous marriage into prehistory, well beyond the earliest instances documented in the historical record...." (http://www.ncbi.nlm.nih.gov/pubmed/21453006)
The point I wish to make is that marriage is primordial and seems to be "built into" human nature. The modern civilized nation-state did not invent marriage and in my opinion does not have the authority to define or redefine it; certainly not at the federal level.
In fact, Justices Kagan, Kennedy, and Sotomayor indicated as much, and Sotomayor said (quoted in Chicago Tribune): "What gives the federal government the right to be concerned at all about what the definition of marriage is?"