Oh, for Pete's sake, you've got the question backwards.
Why do you think getting the government involved in marriage would be an improvement. Do we really need governmet to regulate our private lives?
Since I, as the vast majority of the population do, believe that marriage and family is the cornerstone of a well-functioning society, I believe that it is one of the legitimate areas for some kind of government regulation.
There is nothing to stop people from having whatever kind of living arrangements they want.....just don’t have the government sanction it as being on equal terms with a marriage between a man and a woman.
You and the supporters have it backwards.
Congress shall make no law respecting and establishment of religion. . .
Marriage is an establishment of religion.
Government cannot protect or attack marriage. It is an institution of the church. Judges affirming a new definition of marriage or legislative votes all violate the civil rights found in the first amendment.
This is the intrusion. Will is probably right about DOMA but that is also why all of the government changes to marriage definitions are unconstitutional as well.
Separation of church and state NEVER protects the church. It apparently always protects the State and its ideological preferences.