Everybody knows that double standards are bad. We detest politicians who invoke "sacred" principles that support what they want to do but ignore them when that is convenient.
Parodying this, Groucho Marx observed that "Those are my principles, and if you don't like them ... well, I have others."
But sometimes single standards can be inappropriate.
American courts have caused themselves major problems by trying to find a single standard for applying the Fourteenth Amendment's clause saying that "no state shall ... deny to any person the equal protection of the laws."
The problem is that the word "laws" is used by the Constitution with two distinctly different meanings, but "equal protection" is only meaningful when applied to one of those meanings.
"Law" in one sense — its most fundamental sense — is a general rule of action enforceable by sanctions. An example of law in this sense: anybody who produces counterfeit money will be imprisoned.
"Law," in the Constitution's other sense, states the terms on which the government will enter into a voluntary association. It regulates government's ability to become a party to contracts and other voluntary associations, which are established by mutual consent of all parties to exchange or transfer inducements. For clarity, my periodic table of human associations refers to "law" in this sense as "bylaws."
The key parts of the Hatch Act are an example of bylaws. They forbid federal civil servants, who are in a voluntary employment relationship with the government, from engaging in certain kinds of partisan politics. The maximum punishment is the loss of the civil service job — not a sanction but a withdrawal of inducements.
Confusion results from the fact that Congress uses the same procedures to enact both kinds of laws.
The problem is that "Equal protection of contract" (or other type of voluntary association) makes no sense. Contracts and other voluntary associations to which government can be a party require mutual consent of all parties, parties which inherently must have a right not to consent for any reason. There is no way that "equal protection" could have any meaning here, let alone be a basis for judicial intervention.
The equal protection clause, most simply understood, just forbids enactment of pseudolaws, rules inflicting sanctions (deprivations of life, liberty, or property) on people who have not violated a genuine law. A historical example of such abominations: rules requiring minority individuals to ride in the back of the bus, clearly not a general rule applying to everybody.
Any genuine law automatically meets this generality standard and there is no basis for further inquiry as to whether it violates the Equal Protection clause.
Failure of the courts to recognize this point has led them to try to articulate standards applicable to law in both of its constitutional senses, which is impossible. This is where legal jargon like "rational basis," "strict scrutiny," and "compelling state interest" come in. What do these mean? Don't ask!
Courts using these very flexible "standards" engage in complicated "weighing and balancing" of conflicting considerations. This creates so much confusion that courts can apply appropriately different standards to the two types of law without acknowledging that they are doing any such thing.
It is thus that they can uphold the Hatch Act, a bylaw prohibiting civil servants from giving a partisan political speech, when a law imposing sanctions for doing the same thing on people in general would clearly violate the First Amendment's free speech clause.
These flexible "equal protection" standards do allow the courts to decide most cases correctly. But they are troublesome because they also allow the upholding of pseudolaws if courts consider them necessary to pursue a compelling state interest, an incorrect result if all pseudolaws are unconstitutional.