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.