Ted Olsen, a lifelong and prominent Republican, is leading the legal case to overturning Proposition 8 in California (that would mean he fighting to get gays and lesbians the right to marry). He makes the conservative case for same-sex marriage in Newsweek, something I found through Andrew Sullivan's emotional post. The whole thing is well worth a read, but here is a money quote:
Conservatives and liberals alike need to come together on principles that surely unite us. Certainly, we can agree on the value of strong families, lasting domestic relationships, and communities populated by persons with recognized and sanctioned bonds to one another. Confining some of our neighbors and friends who share these same values to an outlaw or second-class status undermines their sense of belonging and weakens their ties with the rest of us and what should be our common aspirations. Even those whose religious convictions preclude endorsement of what they may perceive as an unacceptable "lifestyle" should recognize that disapproval should not warrant stigmatization and unequal treatment.
When we refuse to accord this status to gays and lesbians, we discourage them from forming the same relationships we encourage for others. And we are also telling them, those who love them, and society as a whole that their relationships are less worthy, less legitimate, less permanent, and less valued. We demean their relationships and we demean them as individuals. I cannot imagine how we benefit as a society by doing so.