In 2000 Vermont became the first state to legally sanction homosexual relationships under the term “civil unions.” Civil unions offer homosexual couples most of the rights and privileges of marriage, including protections in inheritance, property division, child custody and visitation, state tax benefits, and family leave. However, many activists contend that while the civil union is a significant achievement in the fight for gay rights, it excludes same-sex couples from true marriage. Marriage is a fundamental human right, they argue, and restricting true marriage to heterosexual couples discriminates against gays and lesbians.

According to journalist Andrew Sullivan, “The civil union essentially creates a two-tiered system, with one marriage model clearly superior to the other.” In this sense, Sullivan argues, the civil union/marriage system parallels the “separate but equal” policy that governed race relations in...