[Edit: I have been reading a bit about DOMA and the legal issues around it. From what I have seen thus far, I think there is a good case for regarding it as unconstitutional, on the grounds that the federal government was taking to itself rights that were the prerogative of the states to determine, though not on any grounds relating to a constitutional requirement to recognise SSM. On the specific question of whether DOMA is justified, then, the answer to the question in the thread title is perhaps 'no' - but actually I don't think that was the intent of the question being asked. (And that having been said, it seems that there may well be a constitutional paradox, since effectively the choice by one state to legalise SSM may be forcing every other state and the federal government to legalise it whether they want to or not, which must itself be a violation of states' rights. All the arguments around this suggest that the definition of marriage should be a federal rather than a states' issue, because of the injustices that arise within the country if different states have different definitions. If that were the case, then there is no reason why DOMA ought not to stand, and be enforceable in every state, since it is the federal statute. But I'm not an expert and have only been looking into it a short time.)
I have also been arguing as though SSM is not legal in the US - I hadn't realised that actually most of the states have now legalised it; I thought only a few had. The issue with which I am dealing then is that of whether, prior to the enactment of statutes legalising SSM, there was any constitutional or legal or moral requirement for any states to legalise it.]
Ok, there are a lot of different bits of a lot of different arguments flying about. I want to try to understand what are the actual points of disagreement, so I can focus in on those. Perhaps you would be good enough to look through the list of statements below, and indicate whether you agree of disagree with each one. If you agree, a simple 'yes' is sufficient. If you disagree, a 'no' with a brief explanation as to why would be helpful.
1) There is no constitutional reason why a state could not choose to introduce SSM.
True.
2) There is no constitutional reason why a state could not choose not to introduce SSM.
This is a double negative, could you clarify?
3) If (1) and (2) are true, then the question of introducing SSM or not is a matter for the legislature rather than the courts.
False dichotomy. There is another option, the will of the people.
4) When making changes in the law, the onus is on those proposing the change to prove it is a good change, rather than on those opposing the change to prove it is a bad one.
Yes, but once that has been done, the onus shifts to the opposition to explain (using secular reasoning in the US) to explain why it the change is not a good one. As same-sex marriage will have aboslutely no impact on the ability of two biological parents to raise their children, child-rearing as a reason to oppose same-sex marriage fails this test.
5) Marriage is not defined in statute.
In the US, many states enacted statutes defining marriage as between one man and one woman. Most of these have been overturned as violations of the Equal Protection Clause of the 14th Amendment to our Constitution.
6) Until the latter part of the 20th century, when people used the word 'marriage' within the English-speaking world, unless specifically qualified, both the speakers and listeners would have assumed that what was being referred to was a union of a man with a woman.
True but not relevant. Until the latter part of the 20th century, the word "gay" was a euphemism for happy and/or joyful.
7) Homosexual couples are not biologically capable of having children of whom both partners are the biological parent.
True but irrelevant. Many types of marriage consist of partners who are not biologically capable of being the biological parents of any children.
8) The institution of marriage most probably came about in order to provide the optimal context for the raising of children.
Possibly true for the religious institution of marriage but government recognition of marriage had more to do with property rights and securing alliances.
9) The key features of traditional marriage (one man and one woman for life, with the exclusion of close relatives and the mentally incompetent) would be requirements for an institution designed primarily to provide the optimal conditions for raising children, but would not be requirements for an institution designed primarily to provide a context for the partners to express their love to each other.
No. Being raised by biological parents is not always the optimal environment for raising children nor has "one man and one woman for life, with the exclusion of close relatives and the mentally incompetent" ever been a
requirement for traditional marriage.
10) Those couples currently able to marry who are not capable of having children differ in this regard from a typical married couple as a difference of degree, not a difference in kind. (That is to say, there exists a continuous spectrum between those who are fully willing and capable of bearing children within their marriage and those entirely incapable and/or unwilling, such that placing a dividing line at any point would be arbitrary.)
True, which is why placing the dividing line at same-sex couples is arbitrary. Same-sex couples who cannot marry are no different in kind than a couple who can not have children due to age, injury, or choice.
11) All other things being equal, children are best raised by their two biological parents living together in one family.
Provisionally true but irrelevant to the issue of same-sex marriage.
12) If the purpose of marriage is understood as being to provide a context to publicly demonstrate the love of the partners for each other, there is no reason to limit the number of partners to two, nor to limit it to unrelated partners.
True, and if the legal framework of marriage can be changed to accommodate more than two people at a time, go for it.
The bit about related partners will always be debated due to the massive potential for undue influence on the part of one of the parties over the other(s).