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.

It's pathetic how some will decry "activist judges" in matters such as gay marriage but if you bring up the landmark Brown vs The Board of Education of Topeka to them, they quickly try to find justification.

Arizona wouldn't have had to enact their laws if the Federal Government actually enforced existing laws and went after the employers of illegal labor.  Since those employers line the coffers of these politicians, that's  not going to be happening anytime soon.

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This fell out of my fingers but I think an artful writer could make a compelling preliminary statement from it:

"If this Court finds DOMA is constitutional it is essentially findng that homosexuals in marriages, civil unions or other legally recognized committed relationships may be treated differently at law; it is holding that our Constitution allows for Separate and Unequal application of the law to Homosexuals. Such a finding cannot be consistant with the spirit of either our Constitution or the principle that "all [persons] are created equal" and the inalienable rights of "life, liberty, and the pursuit of happiness" is more than a promise but, like marriage itself, a commitment."