Really, I have two arguments against the proposition, but they are so intertwined and impossible to separate that I will have to address them together to some extent but will also try to keep them relatively separate. The two arguments surround religion and law together in ways that I find impossible to separate, yet unwilling to combine.
BLUF (bottom line up front)-- The Government has no role in religious marriage. Their role is in civil marriage, which is really civil union, and the proper role of government would be from the public health and safety perspective; and I argue that God does not want his "rules" legislated, so legislating religious marriage is in opposition to true Christian life. So-- here we go.
Assuming those reading believe that the Bible lays out marriage as being a commitment [before God] between a man and a woman (I am not saying it does or doesn't, but rather that is the argument many make), no license is required for said commitment. Government interference brings the requirement the permit/license for marriage.
In the Loving's case, "Judge Leon Bazile said that God never intended for the races to mix, so their marriage was an abomination."
This is also the case that many make in opposition to two persons of the same sex marrying. It's not as God intended. Well, enter the First Amendment of the Constitution.
"Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof..."
- "As to religion, I hold it to be the indispensable duty of all government, to protect all conscientious professors thereof, and I know of no other business which government hath to do therewith…
Both texts make it clear [to me] that the Federal Government need not restrict religion or the lack of religion in our lives, so whether or not God intended for same sex couples to be together is inconsequential to the government's role in civil marriages.
[My son is crying. I have more, but that means a part III!]