Now that a number of state courts have refused to redefine marriage to include same-sex unions, cries of "discrimination" are being heard.
The "equal protection of the laws" provided by the Constitution of the United States applies to people, not actions. Laws exist precisely in order to discriminate between different kinds of actions.
When the law permits automobiles to drive on highways but forbids bicycles from doing the same, that is not discrimination against people. A cyclist who gets off his bicycle and gets into a car can drive on the highway just like anyone else.
In a free society, vast numbers of things are neither forbidden nor facilitated. They are considered to be none of the law's business.
Homosexuals were on their strongest ground when they said that the law had no business interfering with relations between consenting adults. Now they want the law to put a seal of approval on their behavior. But no one is entitled to anyone else's approval.
Why is marriage considered to be any of the law's business in the first place? Because the state asserts an interest in the outcomes of certain unions, separate from and independent of the interests of the parties themselves.
In the absence of the institution of marriage, the individuals could arrange their relationship whatever way they wanted to, making it temporary or permanent, and sharing their worldly belongings in whatever way they chose.
Marriage means that the government steps in, limiting or even prescribing various aspects of their relations with each other -- and still more their relationship with whatever children may result from their union.
In other words, marriage imposes legal restrictions, taking away rights that individuals might otherwise have. Yet "gay marriage" advocates depict marriage as an expansion of rights to which they are entitled.
They argue against a "ban on gay marriage" but marriage has for centuries meant a union of a man and a woman. There is no gay marriage to ban.
Analogies with bans against interracial marriage are bogus. Race is not part of the definition of marriage. A ban on interracial marriage is a ban on the same actions otherwise permitted because of the race of the particular people involved. It is a discrimination against people, not actions.
Justice Oliver Wendell Holmes said that the life of the law has not been logic but experience. Vast numbers of laws have accumulated and evolved over the centuries, based on experience with male-female unions.
There is no reason why all those laws should be transferred willy-nilly to a different union, one with no inherent tendency to produce children nor the inherent asymmetries of relationships between people of different sexes.