Marriage is an act of union between two people who commit to spend their lives together. It is a voluntary act between two consenting adults that needs no sanction from the state. If the couple desires a religious blessing to be bestowed on that union, they are free and able to proffer the clergy of their choice to receive that blessing.
The state wishes to consolidate it's power in any and every way possible. The fact that a requirement exists not only to receive state sanction [in most cases, but not all], but to be taxed for the privilege of that sanction speaks volumes.
Of course, we know the reason behind DOMA in the first place. It was designed overtly and specifically to keep homosexuals from entering into a union of matrimony, a union that fundamentalist Christians believed to be in their purview and theirs alone. To defend that argument, they rely on the intellecually debunked assertion that 'gay' marriage somehow harms or 'tears apart' heterosexual marriage.
But you don't see the hypocrites arguing to outlaw divorce.......