During the arguments for the Prop 8 case, Scalia said the following:
JUSTICE SCALIA: Mr. Cooper, let me — let me give you one — one concrete thing. I don’t know why you don’t mention some concrete things. If you redefine marriage to include same-sex couples, you must — you must permit adoption by same-sex couples, and there’s – there’s considerable disagreement among — among sociologists as to what the consequences of raising a child in a — in a single-sex family, whether that is harmful to the child or not. Some States do not — do not permit adoption by same-sex couples for that reason.
It’s obvious to anyone familiar with the scientific literature that Scalia is either ignorant or lying: to pick just one of many, the American Academy of Pediatrics recently released a statement:
A great deal of scientific research documents there is no cause-and-effect relationship between parents’ sexual orientation and children’s well-being, according to the AAP policy. In fact, many studies attest to the normal development of children of same-gender couples when the child is wanted, the parents have a commitment to shared parenting, and the parents have strong social and economic support. Critical factors that affect the normal development and mental health of children are parental stress, economic and social stability, community resources, discrimination, and children’s exposure to toxic stressors at home or in their communities — not the sexual orientation of their parents.
According to the policy statement, the AAP “supports pediatricians advocating for public policies that help all children and their parents, regardless of sexual orientation, build and maintain strong, stable, and healthy families that are able to meet the needs of their children.”
But what if Scalia were correct? What if there actually was sufficient debate among experts and a sufficiently contradictory evidence so that we could not draw any scientific conclusions regarding the effect of gay parents on children? Then, in the absence of any evidence to sway the probabilities in any single direction, we’d be left with three equally likely possibilities (on average): negative effect, no effect, or positive effect. In which case it is more likely that there is either no effect or a positive effect than that there is a negative effect.
So even if Scalia were correct, even if we ignore all the scientific evidence (which would weight the probabilities further against “negative effect”), still we find that it is less likely for gay parenting to have a negative effect, on average, than not. Of course, he doesn’t acknowledge this, bundling two cases (positive effect or no effect) into one, and with masterful sleight of hand implying that the probabilities are equal, thus implicitly attempting to grant a stronger probability to the case of negative effect. Unfortunately for him, math just doesn’t work that way.