On this site I have tried to explain in detail my views on same-sex marriage. Among other reasons I have given for my support, and upon which I have elaborated over the course of countless posts, are that I find the use of gender classifications unwarranted and problematic, I think that marriage would greatly benefit children of same-sex couples, and it would help society and the families involved by promoting and protecting stable and secure relationships. Here and elsewhere I have heard these arguments brushed aside by the remark that they are "just as applicable to other family arrangements that are also denied a right to marriage". This is a strange sidestep. For it says nothing about the arguments themselves, for example whether allowing same-sex couples to marry would indeed promote stable and secure relationships or whether that would be a good thing. Instead it merely asserts that the arguments could also be used in favor of allowing other couples to marry who are now currently prohibited. If this were true, then we would have arguments in favor of allowing those couples to marry. Presumably those making this claim, though, find something problematic in allowing these other couples to marry. So even though there are arguments in favor of allowing them to marry, there must also be arguments against allowing them to marry which outweigh these. Now perhaps there are also arguments against allowing same-sex couples to marry that would outweigh these as well. But then those arguments should be presented and weighed against these arguments in favor. Simply saying these arguments could be used elsewhere does nothing to deny that they are arguments in favor of allowing same-sex couples to marry.
That being said, are these arguments really "just as applicable" to other couples? Well let's examine each in turn.
No other couple is being denied the ability to marry based on gender classifications. So that argument can't be directly applied to other couples. The claim must be that a different equal protection argument could be made. What is the classification involved in those cases? Preexisting familial relationships. Now it seems strange to argue that we should be just as skeptical of this type of classification as we are of gender classifications. Hence many state constitutions have provisions like Massachusetts:
Equality under the law shall not be denied or abridged because of sex, race, color, creed or national origin.
It would be especially strange here, though, when those making this claim (that the state should be skeptical of classifying based on familial relationships) would then turn around and ask the court to recognize their familial relationships.
What about children? We are reminded that a parent and grandparent might also be raising a child together. Is that comparable to the case of two parents who adopted a child together? Of course not. In the former case there is one parent and the other person already has a formal relation to the child, grandparent. It is the parent who has primary and ultimate responsibility for the child. This is not the case with the child with two parents who have an equal responsibility to the child and must decide together what is best for their family. But I have also argued the benefit marriage would provide for a child in the situation of a parent and stepparent. Is the grandparent at least comparable to a stepparent? While this comparison is certainly more apt than the comparison to a parent, there are still some differences that are quite relevant here. Consider the case of a single parent who finds someone with whom he she becomes seriously involved to the point of them living together. That relationship could certainly impact the child, and I would venture it would be better for the child for the newly formed family to be stable and permanent. They should all be able to live with the expectation that the relationship will last and that the stepparent is not just a temporary visitor in the child's life. This would be better for the child than a steady stream of boyfriends or girlfriends moving in and moving out. Do we have the same situation with a grandparent? No. For one thing there won't be a steady stream of grandparents moving in and moving out. Secondly the relationship between the parent and grandparent (his or her parent) is already a well established and secure relationship. Even if they reach a point where the grandparent no longer lives with the family, he or she is still likely to be a part of the child's life. I would say that it would be a very bad idea if we made the relationship between grandparent and child dependent on the the parent and grandparent forming a new exclusive bond.
What about the notion of stable and secure relationships? Do we want relationships between family member to be stable and secure? Of course, but we don't need marriage for that and the idea it is necessary could make other family relationships less stable and secure. The key difference is that marriage makes new family. Close family members already have relationships with legal and cultural implications that are formed generally from birth. When a couple marries it is part of the process of two people who came to know, love, and trust each other making a commitment to become a family and take on these new obligations to care for each other. The key to this is the promise of permanence. As Maggie Gallagher and Linda Waite write in their book, The Case for Marriage, write:
The promise of permanence is key to marriage's transformative power. People who expect to be part of a couple for their entire lives--unless something awful happens--organize their lives differently from people who are less certain their relationship will last. The marriage contract, because it is long-term, encourages husbands and wives to make decisions jointly and to function as part of a team. Each spouse expects to be able to count on the other to be there and to fulfill his or her responsibilities. This expectation of a long-term working relationship between husband and wife leads to substantial changes in their behavior, of which the most important is, perhaps, what economists call specialization.
But relationships with other family members (parent-child or sibling) are already expected to be permanent. They know from day one that it is expected to be permanent and don't need to undergo this transformation at some later point. (And the idea that they do, could weaken the security of existing relationships). Nor are such relationships based on the same emotional connection as marriage. Again as Gallagher and Waite write:
To be successful, marriage needs to meet some of the emotional needs of the partners. Individuals may have many emotionally fulfilling relationships--with children, with parents, with their siblings, or with friends. But the emotional relationship that underlies marriage is fundamentally different from these because of the couple's exclusive sexual bond.
So I don't buy the claim that these arguments apply just as well to other couples who cannot marry, and even if they did that does not make the arguments any less valid. The more this issue is debated, the more it seems that the promise of permanence is going to be key to the discussions. Those who support marriage (or at least civil unions) believe that it is also important for many reasons for gay and lesbian relationships to undergo this transformation. It is the one of the key differences between marriage and cohabitation. Those that oppose even civil unions generally don't want gay and lesbian relationships to ever take on this promise of permanence. They view heterosexuality as the ideal that all should strive towards, and for such relationships to undergo this transformation would be to acknowledge their permanent rejection of heterosexual relationships. To people with such views there is not much that I could say to change things. They may come to see things differently someday, but it won't be because of what I write, rather it will be because of who they know.