Last week, the Vermont legislature overrode the governor to legalize gay marriage. The week before, the Iowa Supreme Court achieved the same result by overriding the state legislature, declaring a 1998 ban on same-sex marriage unconstitutional.

For those who agree (as I do) that the benefits of civil marriage should be available to all couples regardless of sexual orientation, does it matter how we get to that destination? I think it does, because the approach taken in Iowa, although liberty-enhancing in this case, ultimately undermines a constitution’s ability to constrain government action and protect individual freedom.

The seven-member Iowa Supreme Court unanimously ruled that limiting marriage to heterosexual couples violates the state constitution’s guarantee of equal protection, which it said “is essentially a direction that all persons similarly situated should be treated alike.” It seems safe to say that neither the constitutional convention delegates nor the voters who approved this provision in 1857 would have agreed that two people of the same sex and two people of opposite sexes were “similarly situated” and “should be treated alike” under civil marriage laws.

In fact, that remains a minority opinion in Iowa. Last month, a University of Iowa survey found that only 26 percent of Iowans supported gay marriage.

The Iowa Supreme Court overrode the majority’s view by reinterpreting the equal protection clause to mean something it did not mean when it was adopted. “Our responsibility,” the justices explained, “is to protect constitutional rights of individuals from legislative enactments that have denied those rights, even when the rights have not yet been broadly accepted, were at one time unimagined, or challenge a deeply ingrained practice or law viewed to be impervious to the passage of time.”

Here we are not talking about applying a constitutional provision in a way consistent with the original public understanding of it (for example, by extending the First Amendment to television or the Fourth Amendment to electronic records). We are talking about applying a provision in a way the people who ratified it would have rejected. How can a right that was “unimagined” in this sense be a constitutional right?

According to the court, “equal protection can only be defined by the standards of each generation.” But if the justices had defined equal protection by the standards of this generation (in Iowa, at least), they would have let the gay marriage ban stand.

“The point in time when the standard of equal protection finally takes a new form,” the court said, “is a product of the conviction of one, or many, individuals that a particular grouping results in inequality and the ability of the judicial system to perform its constitutional role free from the influences that tend to make society’s understanding of equal protection resistant to change.” Let’s be frank: Under this approach, it does not take “one, or many, individuals” to change the meaning of the constitution. It takes exactly four.

As the court noted, legislatures draw distinctions between groups all the time. They establish criminal penalties, impose age restrictions and set conditions for government benefits. If such policy judgments violate equal protection whenever four justices disagree with the reasoning behind them, the line between what judges do and what legislatures do begins to disappear.

Worse, this sort of result-oriented jurisprudence cannot be confined to decisions that limit government and expand freedom. If courts can reach “a new understanding of equal protection” that renders invalid heretofore constitutional laws, they also can reach a new understanding of the First Amendment, allowing restrictions on political speech in the name of fighting corruption, or the Commerce Clause, allowing the federal government to intervene in areas previously reserved to the states or the people.

In these and other cases, changing conditions are said to require reinterpretation, and since no constitution is perfect, you or I may occasionally like the results. But over the long term we cannot count on an evolving constitution to protect our rights.

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