First, I haven't seen compelling evidence that suggests the benefits of a reduction in birth rates a State receives from childless marriages overwhelms the burdens placed upon the State by the cohabitation of the married couple. Let alone being denied the potential contributions to the State the children could make should they actually be born.
Second, the adoption question is an open one. There's no conclusive proof (yet) that children are better off being raised by a couple who do not fit the conventional mother/father roles. That may well be the case. We're in the midst of an experiment with the next generation. But it's far too early to make a claim about benefits or costs associated with being raised in a household headed by a same-sex couple. There simply is no conclusive evidence that the State receives the benefit of better performing citizens when those citizens were raised by same-sex couples as there is when they are raised by their biological parents. Until such evidence is presented, adoption by same-sex couples cannot be fairly characterized as either a benefit or a cost to the State.
Second, the adoption question is an open one. There's no conclusive proof (yet) that children are better off being raised by a couple who do not fit the conventional mother/father roles. That may well be the case. We're in the midst of an experiment with the next generation. But it's far too early to make a claim about benefits or costs associated with being raised in a household headed by a same-sex couple. There simply is no conclusive evidence that the State receives the benefit of better performing citizens when those citizens were raised by same-sex couples as there is when they are raised by their biological parents. Until such evidence is presented, adoption by same-sex couples cannot be fairly characterized as either a benefit or a cost to the State.