I think this is quite right: ” the court of appeals’ limiting principle seems more than a little disingenuous; surely the validity of treating same-sex and opposite-sex couples differently with respect to the right to marry should not turn on the order in which the difference arose, much less on the happenstance of a short-lived court decision overturned by the people.”

This is what I meant when I wrote that this aspect of the decision was too cute by half.  To put it another way: there is zero daylight between the 9th Circuit’s ruling and a ruling that a ban on gay marriage is unconstitutional under equal protection law once a state recognizes gay civil unions. The very same reasoning which finds that this law, enacted in this order, is unconstitutional—namely, that there is no rational basis for the law, and that the optimal parenting and procreation theories do not work, at least in a state which has given gay couples every other right—would compel a finding that a ban on gay marriage is unconstitutional even in a state which never recognized gay marriage.

It should not be the happenstance of the order in which a state recognizes equal rights for same sex couples which dictates the scope of that right.

So if Justice Kennedy sees it the same way—that the order of enactment cannot matter—then he will need to address the heart of the question.  And if he is convinced that the law is the result of animus, then the question of the level of scrutiny to apply to the law could be at play, and the Prop. 8 proponents would have to point to actual evidence that the law furthers the optimal parenting or procreation roles.  And on this record this would appear very tough to do, at least as is evident from Judge Smith’s dissent.