To which the only proper response is: check your premise. It is false. Restrictions on consensual incest, polygamy, polyandry, or even noncontroversial issues such as zoning represent direct restrictions on individual license. But rights aren't license. Those who claim gays have a "right" to "marry" people of their own gender are arguing in favor of a fundamental right which no civilization has recognized since the advent of marriage itself. Hardly a convincing point.
In fact, the argument for gay marriage is fundamentally an argument against civilization, and against the notion of rights that advanced civilizations properly recognize. The elevation of any particular deviancy to the status of normative behavior is an attempt to widen normative behavior so that it becomes meaningless. The elevation of licenses to rights (health care is a right, education is a right, progressive taxation is a right asserted by the poor against the rich, any form of consensual sexual behavior in privacy is a right, ad nauseum) cheapens the things that really are rights.
Our understanding of rights is now so fundamentally diluted that we have Supreme Court Justices holding that there is a "right" to homosexual sodomy, which appears nowhere in the Constitution, but no right to freedom of speech during a political campaign, even though it explicitly appears in one of the most hallowed places of that document.
True. But here's my reasoning: Marriage is a legal contract. And a gay civil union would be a legal contract as well.
Good post, now how do you define institution?