But the court didn't stop there. Kennedy went on to identify a constitutionally protected zone of personal liberty beyond the reach of the government involving the most intimate and private aspects of human relationships.
"Our laws and traditions afford constitutional protection to personal decisions relating to marriage, procreation, contraception, family relationships, child rearing, and education," he wrote.
Kennedy added: "Persons in a homosexual relationship may seek autonomy for these purposes, just as heterosexual persons do."
Despite Kennedy's disclaimer that the Texas decision was not about same-sex marriage, the opinion had an immediate and profound effect on the debate over the issue. Within five months, the Massachusetts Supreme Judicial Court declared that same-sex couples in the state enjoyed a fundamental right to marry under the Massachusetts Constitution. It thus became the first state in the US to establish a state-based constitutional right to same-sex marriage.
The first and most frequently cited case in the Massachusetts decision: Lawrence v. Texas. In the years since, eight other states and the District of Columbia have recognized same-sex marriages. At the same time 30 states passed constitutional amendments defining marriage as a union between one man and one woman. Eight other states adopted statutes enforcing the same traditional definition.
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To prevail at the high court, supporters of California's Prop. 8 and DOMA must be able to offer a persuasive justification for treating gay and lesbian couples differently from heterosexual couples.
Because of the Lawrence decision, they can't argue that society views homosexual conduct as immoral. That argument is off the table.
Instead, proponents of the traditional view of marriage argue that the government is entitled to grant preferential treatment to couples of the opposite sex to encourage what it considers the ideal arrangement for raising children: two biological parents in a stable home, providing male and female role models for their own children.