Will vs. Reason and SSM

I think that judicial invalidation of same-sex marriage bans may actually be a disservice to the cause of SSM by allowing opposition to SSM to focus on political legitimacy concerns, rather than the straightforward merits of the cause.  That said, I'm not sure how helpful Fr. Araujo's reason vs. will criticism is because, as Michael P. points out, those labels become very slippery depending on one's view of the underlying merits.  Here is the crux of Fr. Araujo's argument and, in my view, the crux of the entire SSM debate:

While it is true that marriages of the opposite-sex parents of children (who are crucial for the children to be) break up and that many children are born out of wedlock, these facts do not deny the reality that the couples of the opposite sex can do something that couples of the same-sex cannot: i.e., make children. Children need their fathers and their mothers. The fact that this does not always occur because of the dissolution or the absence of marriage does not make the result of single-parent households a desirable one. To assume, therefore, as the majority conclude, that children will be well-served by a same-sex couple which has not brought the child into this world and can provide someone else’s offspring with everything that the child needs is presumptuous. While the same-sex couple may labor very hard at trying to duplicate what the opposite-sex couple can provide on many fronts if they remain committed to one another and the child upon whom they conferred life, they cannot because for the same-sex couple, it is factually impossible.

It could be "factually impossible" for two reasons: 1) because the same-sex couple are not the biological parents of the child; or 2) because both genders are not represented in the same-sex couple.

The first possibility seems to be a very difficult, even dangerous, argument to make to the extent that it marginalizes adoptive parent-child relationships.  Would anyone (especially pro-life advocates) want to tell a birth mother or prospective adoptive parents that the fact of "making the child" is meaningfully relevant to the quality of the care-giving relationship?  I have never observed any distinctions in the quality of the parenting experienced by members of my extended family by birth and members by adoption, and I'm guessing that other families would affirm that observation.

The second reason is a much stronger possibility, in my view, but it is very rarely fully articulated.  It is one thing to recognize that, yes, women as mothers tend to bring different caregiving qualities to the family than men as fathers do, and that this is a good thing.  But as socially grounded gender roles become fuzzier, our confidence in biologically grounded distinctions between the caregiving functions of men and women has become a bit shakier (as has our confidence in the constitutional validity of such characterizations).  

The strongest argument against SSM seems to be, "Look, we're messing with the definition of a very important social institution that has served us well for many years.  Because the idea of two men or two women beings parents together is relatively new, we do not have enough empirical data to say whether children will be better or worse off.  We should not take that risk."  But if people acknowledge the risk, count the cost of excluding an entire class of committed couples from the stabilizing and identity-affirming institution of marriage, and conclude that gender differences are no longer a sufficient basis for that exclusion, does that really represent the triumph of will over reason? 

One further thought: I'm not sure that conservatives should always be afraid of "will" as a prime mover in judicial or political discourse, especially when social "progress" is so frequently hitched to the exercise of enlightened "reason."  Arguments based on history seem to be subtle appeals to will.  United States v. Reynolds (the polygamy case) reads like a discourse grounded in will.  Niebuhr, I would guess, might in some cases be a fan of will over reason.  Isn't it a question, at least in part, of whether the will is tethered to social change or social continuity?