From the opinion:
The Massachusetts Constitution affirms the dignity and equality of all individuals. It forbids the creation of second-class citizens. In reaching our conclusion we have given full deference to the arguments made by the Commonwealth. But it has failed to identify any constitutionally adequate reason for denying civil marriage to same-sex couples . . .
It is undoubtedly for these concrete reasons, as well as for its intimately personal significance, that civil marriage has long been termed a "civil right" . . . Without the right to marry -- or more properly, the right to choose to marry -- one is excluded from the full range of human experience and denied full protection of the laws for one's "avowed commitment to an intimate and lasting human relationship" . . .
The department argues that no fundamental right or "suspect" class is at issue here, and rational basis is the appropriate standard of review. For the reasons we explain below, we conclude that the marriage ban does not meet the rational basis test for either due process or equal protection. Because the statute does not survive rational basis review, we do not consider the plaintiffs' arguments that this case merits strict judicial,scrutiny . . .
The "marriage is procreation" argument singles out the one unbridgeable difference between same-sex and opposite-sex couples, and transforms that difference into the essence of legal marriage. Like "Amendment 2" to the Constitution of Colorado, which effectively denied homosexual persons equality under the law and full access to the political process, the marriage restriction impermissibly "identifies persons by a single trait and then denies them protection across the board."