Suppose that the state's only interest in promoting marriage is to encourage and support procreation. Take that as a given for this argument: you might not agree with that, but that's the position some people take. So given that, the state has NO interest in promoting SSM's, since they aren't involved in procreation - it's got nothing to do with SSM's being a threat of any kind. So your question should be not why doesn't your marriage pose a threat (it doesn't), but why would the state encourage your marriage when it has no interest in it?
But gay couples do procreate; the last couple decades have seen a sharp rise in the number gay couples producing children that wouldn’t have before more rights were given to them. They, like any infertile couple need outside help, but the children would not have life if not for the gay couple’s union.
Besides, the cart is before the horse in this reasoning. People, gay or no, will have children with or without marriage; it’s one of the most compelling human drives. Consider that, on the last census, the states with the highest % of self-identified SS-lead households raising children were not Massachusetts and California; they were Utah, Mississippi, North Dakota, and Texas, despite these states hostility to such families. The percentages were as high as 33% in those states. The state’s interest is in making sure those couples remain responsible for their children, and spouse if they are financially dependent, SS or no
Well, there's actually a fairly simple answer for that: the state is not capable of distinguishing between a marriage like yours where you have chosen to remain childless and a marriage which produces children. People change their minds, you could easily be lying and claim you want children, and on and on. The state should not try to draw a dividing line between different classes of heterosexual couples because it is not qualified or capable of making such a distinction. But the distinction between a heterosexual couple and a homosexual couple is pretty obvious, and the state IS capable of making that distinction.
The states do blood tests for stds, asks some personal questions, and some even have a doctor test to be sure the couple is
infertile for a marriage license. If this is their reasoning (again, if a state only lets some couples marry if they can medically show they are infertile, it is not) they could at least ask if a couple knows if they are missing reproductive organs, say, from removal of a cancerous uterus. Or they could only apply marriage laws if children result.
Also, why pry into a person’s sex and make a dividing line there then? That is a very private matter to some people, and some actually are both (or neither) sex anatomically and genetically and may have a sexual orientation which would cause them to marry both sex throughout their life, even if they self-identify as sex-less.
edited for bad typing...