From page 8 of this decision (PDF):
The fact that this is a case . . . being prosecuted by members of a minority group does not mean that members of the minority group have a greater interest in equal protection and due process than the rest of society. In our society, a variety of citizens of different backgrounds coexist because we have constitutionally bound ourselves to protect the fundamental rights of one another from being violated by unlawful treatment. Thus, we all have an equal stake in a case that challenges the constitutionality of a restriction on a fundamental right.
SCOTUSblog has context and a summary.