Ken Mehlman, former RNC chairman and 2004 campaign manager for George W. Bush, makes the conservative case for gay marriage in today's Wall Street Journal:
Some misperceive the issue of marriage equality as exclusively progressive. Yet what could be more conservative than support for more freedom and less government? And what freedom is more basic than the right to marry the person you love? Smaller, less intrusive government surely includes an individual deciding whom to marry. Allowing civil marriage for same-sex couples will cultivate community stability, encourage fidelity and commitment, and foster family values. ...
Conservatives don't need to change core convictions to embrace the growing support for equal rights for gay Americans. It is sufficient to recognize the inherent conservatism in citizens' desire to marry, to be judged on their work, and not to be singled out for higher taxes or bullying at school. These objectives can be achieved while also protecting religious liberty, as demonstrated by states enacting civil marriage with exemptions for religious institutions.
Mehlman came out as gay in 2010.