"The procreative aspect of marriage—starting and maintaining a family—is something publicly significant and certifiable. As such, it is and should be governed by the laws of the state. But the expressive aspects are the private reasons for marriage, which should not be governed by the laws of the state, however necessary they might be for the private happiness that makes getting married and staying married personally desirable. In today's parlance, these expressive aspects are about 'relationships' rather than being about what in yesterday's parlance were called 'family relations.' Thus one used to carefully distinguish between one’s relatives and one's friends (even when one privately valued the relationship with one's friends more than one's relations with one's family relatives).
"The state has no valid interest in these private relationships and should not, therefore, interfere with them by attempting to govern them in any way. The state should be concerned with marriage’s public effects, not its private affects. We should be wary of ceding control over these emotions to the state, for private affections become distorted when public interest in them inevitably leads to public control of them. The state should no more govern these private relationships any more than it should govern one’s friendships, however long lasting they might be.
"Like the lives of the human beings who have created it, the state seeks its own survival. In order to regularly replenish its citizenry and ensure national continuity, the state has an interest in encouraging procreation and child rearing. Since procreation-with-child-rearing is the only truly public reason for marriage, I think marriage is essentially endorsed and structured by the state to best facilitate the procreation-and-rearing-of-children so born and raised in the society that purposefully maintains and supports that public institution. In general, parents have the primary right to raise the new persons they have brought into the world. Since these parents are responsible for bringing their children into the world and into society, the children have a right to their parents’ attention to them—a claim on their parents to fulfill their parental duty as much as it is possible for them to do. Absent any severe physical, mental, or emotional impediments to parenthood that inevitably lead to abuse or neglect, children are best raised by their natural parents. The state has an interest in respecting and even enforcing the natural claim children have on their own parents. Thus I consider these rights to be natural, in the literal sense of their natal character; and they are natural in the sense of being pre-political and thus not entitlements from the state."
— Rabbi David Novak, "Why We Should Oppose Same-Sex Marriage"