While all parties in these cases agreed that there was a fundamental right to marry, they differed as to whether that right substantively meant marrying the person of your choice, or marrying the opposite-gender person of your choice. The exclusionists argued that a gay man and a straight man both have an equal right to marry a woman, so what are we complaining about? Nonsense, said the Court. Our right to marry the person of our choice is a fundamental aspect of our individual identity and personal autonomy, and saying a gay man has the right to marry a woman is no right at all. The Court repeatedly harkened back to Perez v. Sharp, the landmark 1948 California Supreme Court decision that overturned laws against interracial marriage. They noted that similar arguments were applied then: a person had the right to marry the person of their choice, any white man could choose his own white wife, and any non-white man could choose his own non-white wife. The logic was wrong then, and it's wrong now. Formulating a substantive right so narrowly that it inherently excludes a class of citizens is just discrimination in a semantic disguise, and the Court rightly rejected it.
The Court also dismissed the notion that sexual orientation discrimination was a form of gender discrimination. This argument is often made by gay marriage proponents, because gender discrimination is an established "suspect class" (meaning that courts guard against that kind of discrimination more stringently) while sexual orientation is not. Thus, in order to claim the more protected status, arguments are framed in terms of gender discrimination. A gay man could marry a woman, but not a man, the only difference being the gender of the spouse, so there's gender discrimination going on, or so the argument goes. Not so fast, said the Court. We all understand what gender discrimination is, it's when laws disfavor women and favor men, and that's not what's going on here. What's going on here is discrimination based on sexual orientation, not gender. The Court called a spade a spade. Fortunately, the Court went on to establish sexual orientation as a "suspect class" in its own right (a new precedent), worthy of the same protections as gender, race, and religion. In other words, the Court said that while there isn't any gender discrimination going on here, there is sexual orientation discrimination going on, and that's just as unconstitutional.
While the appellate court had reached the same conclusions about gender versus sexual orientation discrimination, they balked at recognizing sexual orientation as a suspect class, because of the requirement that it be based on an "immutable" trait. The "immutability" of sexual orientation is a matter of some factual dispute, and the appellate judges felt the trial record lacked appropriate fact-finding to reach a legal decision on that. The Supreme Court, applying some common sense, reasoned that they did not need to find scientific certainty of biological immutability for their legal purposes. They noted that religion is among the recognized "suspect classes", and nobody would claim that you're born a particular religion and can't choose to change. Rather, because a person’s religion is so integral an aspect of one’s identity, it is not appropriate to require a person to repudiate or change his or her religion in order to avoid discriminatory treatment. Sexual orientation, the Court recognized, is "immutable" in the same way that religion is.
On a technical side argument, the Court eschewed the hairsplitting that gay marriage proponents had been spinning in regard to "Prop 22", the 2000 ballot initiative that said "Only marriage between a man and a woman is valid or recognized in California." This initiative statute was passed at a time when Californians were afraid they might be forced to recognize out-of-state gay marriages (Hawaii was the big threat at the time), and the language was placed in the legal code at a point that was describing recognition of marriages from outside jurisdictions. Gay marriage proponents, splitting hairs, claimed that the placement of the language meant that it only applied to California's recognition of gay marriages from outside states, and thus it did not preclude the California legislature from legalizing gay marriage within the state. Twice, the California legislature has passed such a bill, and twice Governor Schwarzenegger has vetoed it, saying that it violates the will of the people as expressed in Prop 22. (His position was that either the people had to overturn their own initiative, or the Court had to rule it unconstitutional, but either way, it was not up to the Legislature.) The Supreme Court opinion fully validated the Governor's position. Even though they ultimately rejected "Prop 22" as unconstitutional, they took the time to note that Prop 22 would have been interpreted to govern all marriages in California, and not just out-of-state ones. The clear implication being that had the Governor signed the Legislature's gay marriage bills, the Court would have shot them down as being in conflict with Prop 22 (which being a voter initiative, would take precedence over legislative action). No hairsplitting for this Court.
Finally, the Court gave a robust and common-sense rejoinder to the question of what's in a name. The Court noted the overall context of the question at hand, in that California has created a legal category called "domestic partnership", which is open to same-sex couples, and which gives domestic partners all of the same rights and responsibilities as spouses. So, the Attorney General asked, if the state provides all of the same rights and responsibilities to same-sex domestic partners as it provides to opposite-sex married couples, and the only difference is the name ("domestic partnership" vs "marriage"), isn't that equal protection of the law? No, said the Court, as we have learned from history, "separate but equal" is not equal. By reserving to one class of persons and denying to another the name with strong traditional and symbolic significance, the Court said that the state was denying equal "dignity, respect, and stature", which are themselves a substantive part of the right to marry. Not only is this a strong symbolic disability, the Court found, but because of the historic disparagement of gay people, the creation of a parallel but separate status is likely to convey a "second class" status, and signal a difference in dignity and respect. Moreover, because the newly minted "domestic partner" status will not have the same recognition and familiarity of marriage, domestic partners are likely to encounter difficulties and complications in the practical exercise of even those rights which are legally conveyed. Demonstrating a substantive understanding of the realities of the situation, the Court recognized that this "mere" difference of nomenclature has far more impact than "just a name".
Thus it was that a Chief Justice with a reputation as a "careful jurist" and a "moderate Republican" was joined by three other judges (two of them Republican) in writing this:
we conclude that, under this state’s Constitution, the constitutionally based right to marry properly must be understood to encompass the core set of basic substantive legal rights and attributes traditionally associated with marriage that are so integral to an individual’s liberty and personal autonomy that they may not be eliminated or abrogated by the Legislature or by the electorate through the statutory initiative process. These core substantive rights include, most fundamentally, the opportunity of an individual to establish — with the person with whom the individual has chosen to share his or her life — an officially recognized and protected family possessing mutual rights and responsibilities and entitled to the same respect and dignity accorded a union traditionally designated as marriage. As past cases establish, the substantive right of two adults who share a loving relationship to join together to establish an officially recognized family of their own — and, if the couple chooses, to raise children within that family — constitutes a vitally important attribute of the fundamental interest in liberty and personal autonomy that the California Constitution secures to all persons for the benefit of both the individual and society. [In Re Marriage Cases, Cal. Sup. Ct. S147999, pp. 6-7]