Like it our not, how my non-Orthodox or non-Christian neighbor lives does have consquences for my life. How, can I/we encourage marital fidelity (which is not only for my neighbor's good, but the common good, and those my good) in those members of society who do not subscribe to any religious tradition? In other words, what can be done in the public square to replace the ontological individualism that is becoming increasingly the norm in society?
My libertarian instincts prompt the following responses:
1) costs imposed on me by my neighbors are not all costs I get to have a say about. Some costs (throwing trash on my lawn, harboring dangerous wild animals) I can address through trespass and nuisance law. But neighbors' marriages, whether sunny or stormy, will rarely produce impacts on me that the law recognizes as actionable. I think that is as it should be - once the state starts acting like a busy body, there's no telling where it will end up poking its nose. So I think there are many depressing aspects of my hypothetical neighbors' lives (my real neighbors are very nice) that I will just have to deal with on my own, without society's aid.
2) there are moral obligations imposed on people by their beliefs that are greater than the legal obligations imposed by society. Thus if a neighbor's marriage is on the rocks or imposing costs on the rest of the neighborhood, private action may be called for. There is a strong trend toward private neighborhood associations, organizations which often do impose constraints (rarely about marriages, usually about landscaping and so on). My friend Bob Nelson has a new book on the topic that is on my desk, awaiting time to savor it. I think this is the sphere in which we must address the concerns Fr. Gregory raises.