With all due respect to Justice Kennedy, pro-big federal government activist Justices cannot afford to reference the 10th Amendment for any reason.
I haven't read opinion yet, but if Kennedy referred to equal protections clause in Section 1 of 14th Amendment then that is a wrong, PC interpretation of that clause.
More specifically, note that regardless of the equal protections clause in Sec. 1 of 14A, note that Sec. 2 of that amendment discriminates on the basis of sex, age and citizenship. In fact, if John Bingham had meant for equal protections clause to be understood the way that activist justices are now interpreting it, then there would have been no need for the 15th, 19th, 24th and 26th Amendments which protect voting rights on the basis of race, sex, taxes owed and age respectively.
Regarding 14A's equal protections clause, the states have the 10A-protected power to discriminate on any basis not protected by an express constitutional right. What 14A's equal protections clause does is to require the states to discriminate equally on criteria not protected by the Constitution.
It's ironic that the equal protections clause of California's constitution is expressly based, I believe, on 14A's equal protection clause.
By seeking to injure the very class New York seeks to protect,DOMA violates basic due process and equal protection principles applicable to the Federal Government. The Constitution’s guarantee of equality “must at the very least mean that a bare congressional desire to harm a politically unpopular group cannot” justify disparate treatment of that group.
Despite the fact that the four liberals allowed Kennedy to couch the majority opinion largely in States' rights arguments, does this sound like the holding of someone who intends to uphold a State's marriage laws if they forbid gay marriage? It does not.
Dissenting (Alito -- correctly -- notes that in defining marriage, DOMA does not infringe on the States' rights to regulate it.)
"It leaves the choice to the people, acting through their elected representatives at both the federal and state levels. The Constitution does not guarantee the right to enter into a same-sex marriage. Indeed, no provision of the Constitution speaks to the issue."
Dissenting (Nino. Who understands the real danger implied in 5th and 14th Amendment arguments offered by the majority):
"It takes real cheek for today's majority to assure us, as it is going out the door, that a constitutional requirement to give formal recognition to same-sex marriage is not at issue here—when what has preceded that assurance is a lecture on how superior the majority's moral judgment in favor of same-sex marriage is to the Congress's hateful moral judgment against it. I promise you this: The only thing that will "confine" the Court's holding is its sense of what it can get away with."
Just so.
I have a rule of thumb you might find useful: When you are on the side of a Constitutional issue that is opposed by Thomas, Alito and Scalia, you are on the wrong side of the Constitution. These men are not gods; they can be wrong. But ALL THREE of them are NEVER wrong at the same time.