In their ruling the California supreme court quoted a decision made in Perez vs. Sharp

'[w]ithout doubt, [the equal protection clause of the California Constitution] denotes not merely freedom from bodily restraint, but also the right of the individual to contract, to engage in any of the common occupations of life, to acquire useful knowledge, to marry, establish a home and bring up children, to worship God according to the dictates of one’s own conscience, and, generally, to enjoy those privileges long recognized at common law as essential to the orderly pursuit of happiness by free men.’”

The Perez decision continued: “Marriage is thus something more than a civil contract subject to regulation by the state; it is a fundamental right of free men.”

--http://en.wikipedia.org/wiki/Proposition_8#2008:_California_Supreme_Court_ruling