Promising equal treatment to some is fundamentally different from promising equal treatment to all.

From Justice Carlos Moreno's dissenting opinion (though technically it was a concurring/dissenting opinion since it agreed with the majority on prior marriages):

The question before us is not whether the language inserted into the California Constitution by Proposition 8 discriminates against same-sex couples and denies them equal protection of the law; we already decided in the Marriage Cases that it does. The question before us today is whether such a change to one of the core values upon which our state Constitution is founded can be accomplished by amending the Constitution through an initiative measure placed upon the ballot by the signatures of 8 percent of the number of persons who voted in the last gubernatorial election and passed by a simple majority of the voters. (Cal. Const., art. II, § 8.) Or is this limitation on the scope of the equal protection clause to deny the full protection of the law to a minority group based upon a suspect classification such a fundamental change that it can only be accomplished by revising the California Constitution, either through a constitutional convention or by a measure passed by a two-thirds vote of both houses of the Legislature and approved by the voters?

snip

The equal protection clause is therefore, by its nature, inherently countermajoritarian. As a logical matter, it cannot depend on the will of the majority for its enforcement, for it is the will of the majority against which the equal protection clause is designed to protect. Rather, the enforcement of the equal protection clause is especially dependent on “the power of the courts to test legislative and executive acts by the light of constitutional mandate and in particular to preserve constitutional rights, whether of individual or minority, from obliteration by the majority.

snip

Denying the designation of marriage to same-sex couples cannot fairly be described as a “narrow” or “limited” exception to the requirement of equal protection; the passionate public debate over whether same-sex couples should be allowed to marry, even in a state that offers largely equivalent substantive rights through the alternative of domestic partnership, belies such a description. “he constitutional right to marry . . . has been recognized as one of the basic, inalienable civil rights guaranteed to an individual by the California Constitution . . . .” (Marriage Cases, supra, 43 Cal.4th at p. 781.) Prior to the enactment of Proposition 8, the California Constitution guaranteed “this basic civil right to all Californians, whether gay or heterosexual, and to same-sex couples as well as to opposite-sex couples.” (43 Cal.4th at p. 782.)

snip

Describing the effect of Proposition 8 as narrow and limited fails to acknowledge the significance of the discrimination it requires. But even a narrow and limited exception to the promise of full equality strikes at the core of, and thus fundamentally alters, the guarantee of equal treatment that has pervaded the California Constitution since 1849. Promising equal treatment to some is fundamentally different from promising equal treatment to all. Promising treatment that is almost equal is fundamentally different from ensuring truly equal treatment. Granting a disfavored minority only some of the rights enjoyed by the majority is fundamentally different from recognizing, as a constitutional imperative, that they must be granted all of those rights. Granting same-sex couples all of the rights enjoyed by opposite-sex couples, except the right to call their “ ‘officially recognized, and protected family relationship’ ” (maj. opn., ante, at p. 7) a marriage, still denies them equal treatment.

snip

Proposition 8 represents an unprecedented instance of a majority of voters altering the meaning of the equal protection clause by modifying the California Constitution to require deprivation of a fundamental right on the basis of a suspect classification. The majority’s holding is not just a defeat for same-sex couples, but for any minority group that seeks the protection of the equal protection clause of the California Constitution.

This could not have been the intent of those who devised and enacted the initiative process. In my view, the aim of Proposition 8 and all similar initiative measures that seek to alter the California Constitution to deny a fundamental right to a group that has historically been subject to discrimination on the basis of a suspect classification, violates the essence of the equal protection clause of the California Constitution and fundamentally alters its scope and meaning. Such a change cannot be accomplished through the initiative process by a simple amendment to our Constitution enacted by a bare majority of the voters; it must be accomplished, if at all, by a constitutional revision to modify the equal protection clause to protect some, rather than all, similarly situated persons. I would therefore hold that Proposition 8 is not a lawful amendment of the California Constitution.

http://www.dailykos.com/story/2009/5/26/735581/-The-Laudable-Dissenting-Opinion-in-Todays-California-Court-Decision