It's as predictable as the arrival of cherry blossoms on the National Mall in early spring: the U.S. Supreme Court weighs the constitutionality of a new law that has substantial popular support and wary proponents of that law start questioning the need for third-party evaluations. Even though this particular kind of evaluation is a pillar of American democracy.

"What I am greatly concerned about is how we as a society have let lawyers, judges and politicians overrule the vote of the people," one letter-to-the-editor writer complained last week.

"We the people can no longer control our destiny," wrote another. "The courts and legislators are trying to take this right away from us."

Both letter writers were inspired by Tuesday's Supreme Court hearing on the legality of Proposition 8, the same-sex marriage ban that California voters endorsed 52 percent to 48 percent just five years ago. Those who are confounded by the high court's meddling in the matter might want to read up on Marbury v. Madison, the 210-year-old Supreme Court decision that established the principle of judicial review.

Write all the laws you want, folks, by way of grass-roots initiative or legislative consensus, but if five out of nine justices say it conflicts with principles set forth in the U.S. Constitution, it means nothing. When your ninth-grade history teacher talked about checks and balances, this is what he was referring to.

In the case at hand, conservatives who oppose gay marriage want the Supreme Court to preserve the "will of the people" and sanctify Prop. 8. Would they feel the same way about voter-endorsed laws that decriminalize marijuana or liberalize immigration policies? Not a chance.

Liberals are equally guilty of this kind of selective, agenda-driven court-bashing -- the nation's head lib included.

Almost exactly a year ago, not quite a week after the Supreme Court heard the last of the oral arguments on the constitutionality of Obamacare, President Obama declared that the Supremes ought not mess with a law properly (if contentiously) voted in by the people's elected representatives in Congress.

"For years what we've heard is the biggest problem on the bench was judicial activism or a lack of judicial restraint, that an unelected group of people would somehow overturn a duly constituted ... and passed law," Obama told reporters. "Well, (the Affordable Care Act) is a good example."

A year later, the Obama administration filed a friend-of-the-court brief calling upon the Court to reject the "will of the people" on gay marriage in California.

The problem with treating the "will of the people" like the Grail of Unwavering Truth is that the people are often just plain wrong. Imagine Alabama voters, circa 1955, considering a ballot initiative that would permit interracial marriage. Or interracial anything.

Consider, too, that the people's collective "will" can morph over time -- sometimes a very short span of time. How do we measure the will of the people when, for example, a new Field Poll says 61 percent of Californians now favor same-sex marriage? Prop. 8 presumably goes back on the books if the Supreme Court declares that states have the right to render such restrictions, but same-sex marriage advocates would then just place another initiative on the ballot asking voters to reverse Prop. 8. And based on the way the wind blows at present, it would pass even more decisively than Prop. 8 did in 2008.

Popular opinion changes. The Constitution does not. Supreme Court interpretations of the Constitution may evolve over time, reflecting public sentiment and the court's ideological makeup, but it moves at glacial speed in comparison to the winds of public opinion. Or, as many of us call it, the will of the people.

Email Editorial Page Editor Robert Price at rprice@