WASHINGTON -- For most of the 53 years since the Supreme Court's school desegregation decision, the court, in collaboration with people who fancy themselves "progressive," has been instructing Americans to unlearn the lesson of those decisions -- the lesson that race must not be a source of government-conferred advantage or disadvantage. Last week the court began rectifying its abandonment of that premise in the name of "diversity."

The court ruled 5-4 that Seattle, which never had school segregation, and Louisville, which did but seven years ago completed judicially mandated remedial measures, must stop using race in assigning children to schools to produce particular racial ratios in enrollments. How did we get from this: "Distinctions by race are so evil, so arbitrary and invidious that a state bound to defend the equal protection of the laws must not invoke them in any public sphere" (the NAACP's brief, written by Thurgood Marshall, in the 1954 Brown v. Board of Education desegregation case), to this: Local public education establishments routinely taking cognizance of race in assigning children to schools?

n 1978, in the Bakke case concerning racial preferences in a medical school's admissions, Justice Lewis Powell wrote that institutions of higher education have a First Amendment right -- academic freedom -- to use race as one "plus" factor when shaping their student bodies to achieve viewpoint diversity. Thus was born the "educational benefits" exception to the Constitution's guarantee of equal protection of the laws. But that hardly justifies assigning 6-year-olds to this or that school solely because of their races.

Twenty-five years after Bakke, in 2003, the court approved the University of Michigan Law School's use of race in admissions, because that use supposedly involves a "highly individualized, holistic review" of applicants. The court simultaneously disallowed Michigan's undergraduate admissions plan that automatically granted preferences based solely on race -- as Seattle has done in high schools and Louisville has done in grades K through 12. Samuel Alito, Antonin Scalia and Clarence Thomas joined Chief Justice John Roberts' opinion for the court, in which Roberts said: "The way to stop discrimination on the basis of race is to stop discriminating on the basis of race." Anthony Kennedy, although agreeing that Seattle's and Louisville's practices are unconstitutional, chastised Roberts for an "all-too-unyielding" opposition to race-based programs. Yet when dissenting in the law school case, Kennedy said: "Preferment by race, when resorted to by the state, can be the most divisive of all policies, containing within it the potential to destroy confidence in the Constitution and in the idea of equality."

Sandra Day O'Connor, writing the majority's opinion in that 2003 case, breezily asserted that in 25 years racial preferences would not be "necessary" to further diversity. But diversity preferences appeal to race-obsessed social engineers -- a cohort particularly prevalent among today's educators -- precisely because the diversity rationale never expires. The diversity project is forever a work in progress. Seattle's "race-conscious" policies were devised by the sort of people who proclaimed on the school district's Web site that "having a future time orientation" (planning ahead), "emphasizing individualism as opposed to a more collective ideology" and "defining one form of English as standard" constitute "cultural racism" and "institutional racism" and arises from "unsuccessful concepts such as a melting pot or colorblind mentality." Stephen Breyer, in a dissent joined by Ruth Bader Ginsburg, David Souter and John Paul Stevens, said the court should be deferential to such people when they shuffle pupils on the basis of race.

Why race? Although progressive people would never stoop to racial stereotyping, they evidently believe that any black or other minority child, however young, or from whatever social background, makes a predictable and distinctive -- you might say stereotypical -- contribution to "diversity."

Breyer said that last week's decision abandons "the promise of Brown." Actually, that promise -- a colorblind society -- has been traduced by the "diversity" exception to the Equal Protection Clause. That exception allows white majorities to feel noble while treating blacks and certain other minorities as seasoning -- a sort of human oregano -- to be sprinkled across a student body to make the majority's educational experience more flavorful.

This repulsive practice merits Clarence Thomas' warning in his opinion concurring with last week's ruling: Beware of elites eager to constitutionalize "faddish social theories." Often, they are only theories. As Roberts said, Seattle and Louisville offered "no evidence" that the diversity they have achieved (by what he has called the "sordid business" of "divvying us up by race") is necessary to achieve the "asserted" educational benefits.

Evidence is beside the point. The point for race-mongering diversity tinkerers is their professional and ideological stake in preventing America from achieving "a colorblind mentality."