And it has been Constitutionally upheld that states have the right to define marriage. That the Constitution protects that right. The judge who ruled on Prop 8 gave an incorrect and inconsistent interpretation of the Constitution. The Constitution doesn't touch on marriage and sexuality, there is no explicit wording that would protect homosexuality or even heterosexuality. Within our Constitutional Republic there is a process to amend the Constitution. If the states amended the Constitution to specifically say that homosexuality is protected and must be defined within marriage, than there would be a specific argument. A federal judge in MA just ruled that DOMA is unconstitutional in MA because the federal government has no right to dictate to the states how to run marriage (and rightly so). The ruling was passed because the state has the Constitutional right to define marriage.
The DOMA decision only ruled that a state has the right to regulate marriage. It does not give a state the right to regulate marriage in a way that violates the Constitutional rights of American citizens or violates the Federal Constitution.
Once again, you are missing vital facts in this case...
The judge determined that the will of the voters in California violated the rights of a minority, same sex couples, guaranteed by the federal Constitution. Those rights were equal protection under the law as guaranteed by the Equal Protection Clause and the right to Due Process. The law is written, "No State shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States; nor shall any State deprive any person of life, liberty, or property, without due process of law; nor deny to any person within its jurisdiction the equal protection of the laws."
Supreme Court precedent holds that marriage is a fundamental Constitutional right...
Taylor versus Safely (1987): "the decision to marry is a fundamental right" and "marriage is an expression of emotional support and public commitment."
Zablocki versus Redhail (1978): "The right to marry is of fundamental importance for all individuals."
Cleveland Board of Education versus LaFleur (1974): "This court has long recognized that freedom of personal choice in matters of marriage and family life is one of the liberties protected buy the Due Process Clause of the Fourteenth Amendment."
Loving versus Virginia (1967): The "freedom to marry has long been recognized as one of the vital personal rights essential to the orderly pursuit of happiness by free men."
The judge defended the will of the people, the federal Constitution; by overturning Proposition 8, which sought to mandate gender roles and restrict same sex couples to a culturally inferior institution by excluding them from marriage and the cultural dignity, respect, and stature inherent in marriage. The state has no interest in excluding one group from a fundamental right without rational basis and so the judge was obligated to overturn it.