Marriage is not a civil right. Marriage is an institution ordained by God in Genesis: "For this reason a man will leave his father and mother and be united to his wife, and they will become one flesh," and reaffirmed by Jesus in Matthew 19:4-6. All societies throughout recorded history have publicly recognized the institution of marriage as a sexually complementary public institution. The government has no business creating an entirely new -- and destructive -- institution and then attaching to it the name of marriage.
Marriage is not solely or centrally about love. It is centrally concerned with children and their connection to their biological parents. The state has no interest or investment in whether couples love each other. If marriage were solely or even centrally about love and had no connection to children, the state would have no interest in being involved with marriage.
The current requirements for government-sanctioned marriage are: 1. Numbers of partners. Marriage is limited to two partners, therefore no polygamous marriages. 2. Consanguinity. Partners cannot be closely related by blood, therefore no incestuous marriages. 3. Minimum age. Partners must be of major age, therefore no pedophiliac marriages. 4. Sexual complementarity. Partners must be of the opposite sexes, therefore no same-sex marriages.
Society for centuries has concluded that these requirements best serve the needs of children and therefore best serve the needs of society. Current marital requirements do not violate civil rights. Once societies sever marriage from both gender and children, its cultural value diminishes. Laws forcing the acceptance of same-sex marriage should be prevented from unilaterally redefining marriage. Legalizing same-sex unions would require explicit public endorsement of the idea that a child really does not need a mother and father.