I think some confusion arises in the debate over same-sex marriage by equating the legal relationship of marriage with the emotional relationship that underlies it. Civil marriage establishes a specific legal kinship relationship by identifying one person as another's spouse which brings about numerous legal obligations and consequences. Underlying this legal relationship is almost always an emotional one characterized by a selfless love which puts the needs of the family--the couple and any children--before one's own desires. We may feel that one should establish the legal relationship if and only if the emotional one is present, but there are legal marriages lacking the emotional connection, and couples with a deep emotional bond who do not marry.
Perhaps one should bear in mind a similar situation with the legal kinship relationship of parent-child. That legal relationship is based on a biological connection. It is possible, though, for one to establish the legal relationship through adoption without the biological connection. When a child is born, in almost all cases, the legal relationship is also automatically established. Regardless of how the legal relatioship is established, though, the parents have the same legal responsibilities and privileges. Likewise, same-sex couples wishing to marry are asking to establish the same legal relationship of marriage with the same responsiblities. It is important to note that same-sex couples are capable of fulfilling all of these legal obligations. The decisive question in the SSM debate is whether there is any justification for prohibiting one from establishing the legal relationship based on the sex of the prospective spouse. Some other questions raised in the debate are interesting in their own right, but peripheral to the central question above. These include....
(HOMOSEXUALITY) Is it possible for same-sex couples to have the same emotional connection as opposite-sex couples? I don't see how anyone who knows some same-sex couples can think the answer is anything other than yes. This leads me to believe that SSM should not only be allowed, but for some couples encouraged. Even if somehow one thought the answer was no, that would only lead possibly to a conclusion that no same-sex couple should get married, not to a conclusion that they should not be allowed to get marry. I have attended weddings where I thought the couple should not be getting married. That does not mean I believe I should have been entitled to legally prohibit their marriage.
(FRIENDSHIP) Should the government offer another legal relatonship basd on the emotional bond of friendship? Note that friends can marry. I married my best friend. Perhaps, though, a separate legal relation should be created with different requirements than marriage. This might be a good policy idea, but we do not have a right to have the governmen create legal relations. As Jim Henley notes the issue in SSM is whether once that legal relation is created, one can deny equal access to it. I should also note that as a culture we can honor emotional relationships without giving them legal effect.
(POLYGAMY, CONSANGUINITY) Is there any justification for using th existence of other kinship relationships to deny the establishment of another? I believe the answer is yes. Without getting into specifics, the problem is the detrimental impact of even the possibility of the new relationship on the existing ones.
(HISTORY) Historically had there been any justification for prohibiting one from designating a spouse of the same sex? Probably. It used to be that the legal role of husband and wife were different from one another. They had different responsibilities and different rights. Thus a woman may not have been capable of fulfulling the legal duties of husband, or a man of fulfulling those of wife. This is not the case today.