John D. Podesta and Robert A. Levy write on the opinion pages of The Washington Post: “Loving v. Virginia ended bans on interracial marriage in the 16 states that still had such laws. Now, 43 years after Loving, the courts are once again grappling with denial of equal marriage rights — this time to gay couples. We believe that a society respectful of individual liberty must end this unequal treatment under the law.”