Wrong question, the right question is it is libertarian for the state to use its’ illegitimate power over cultural institutions to redefine those institutions? Ron Paul does not think so, instead, Congressman Paul favors making sure federal judges don’t once again exceed their power by imposing a new definition of marriage on the people:

“Some may argue that allowing federal judges to rewrite the definition of marriage can result in a victory for individual liberty. This claim is flawed. The best guarantor of true liberty is decentralized political institutions, while the greatest threat to liberty is concentrated power. This is why the Constitution carefully limits the power of the federal government over the states. Allowing federal judges unfettered discretion to strike down state laws, or force a state to conform to the laws of another state, leads to centralization and loss of liberty.

While marriage is licensed and otherwise regulated by the states, government did not create the institution of marriage. In fact, the institution of marriage most likely pre-dates the institution of government! Government regulation of marriage is based on state recognition of the practices and customs formulated by private individuals interacting in civil society. Many people associate their wedding day with completing the rituals and other requirements of their faith, thus being joined in the eyes of their church – not the day they received their marriage license from the state. Having federal officials, whether judges, bureaucrats, or congressmen, impose a new definition of marriage on the people is an act of social engineering profoundly hostile to liberty.”