Child Rape Not A Capital Crime

I reserve judgment on the latest SCOTUS opinion, not having read it, and limit myself to one observation based on the WaPo story. Justice Kennedy is cited arguing for the majority
the absence of any executions for rape and the small number of states that allow it demonstrate "there is a national consensus against capital punishment for the crime of child rape."
Somehow I doubt that logic would hold water for him with regard to same-sex marriage.