In the principle, the Constitution guarantees equal protection of the laws to every person. No individual or group should be denied the equal right to enjoy significant social, political, and economic opportunities on account of race, ethnicity, gender, national origin, creed, disability, and so on. But the abstract principle of equality of treatment is deceptively simple. One aspect of equality requires the state to treat similarly situated people similarly, unless there is some overriding and compelling interest to treat differently situated people differently. A driver's license may be denied to all persons with poor eyesight out of concern for public safety, but not to only visually challenged men because of a bias or stereotype that men drive worse than women. Another dimension of equality requires equal treatment with regard to education, employment, housing, and other important opportunities. Persons should be given an equal footing within the public and private sectors to enjoy the societal goods and resources deemed to provide a meaningful life. Further complicating the equal treatment principle is the presence of competing perspectives of the meaning of equality. Equality of opportunity requires the state to remove any legal barriers operating to discriminate, making sure that persons have the same opportunity to enjoy the goods and resources of society. Equally qualified persons should have the same chance in getting an education, landing a job, or buying a house regardless of whether the end result is that some prevail over others. Equality of outcome, on the other hand, requires the state to remove the legal barriers and lingering effects of discrimination, making sure that all people actually enjoy the goods and resources of society. Past and current prejudice requires the state to take affirmative steps to equalize fairer outcomes in people getting an education, landing a job, or buying a house. This philosophical difference between equality of opportunity and equality of outcome is reflected within the current debate over affirmative action programs.

In the 1960s, the President and later Congress adopted affirmative action remedies to overcome the lingering effects of past discrimination against minority groups and women. Soon after the states, universities, and employers developed affirmative action plans as well. Greater social, economic, and political opportunities were open to groups who had experienced unfair patterns of discrimination. But white males began to challenge such policies as constituting reverse discrimination and giving preferential treatment to less qualified people. The first case to reach the Supreme Court involved a challenge by Allan Bakke, who was a white male and top student at the University of Stanford. He was denied admission two years in a row into the medical school at the University of California, despite having a better grade point average, test score, and interview rating than others who were admitted under an affirmative action plan. In the University of California Regents v. Bakke (1978), the Supreme Court held that this special admission's plan gave preferential treatment to minorities and therefore violated the equal protection clause of the Fourteenth Amendment. But the justices also held that affirmative action programs are not per se unconstitutional. State institutions of higher education may pursue the important interest of achieving a diversified student body by taking race or sex into account as a factor or one of several factors in admitting students. The problem with the medical school, concluded the majority, was that the admissions standards created a racial quota where qualified white students were excluded solely due to their race.

Since Bakke, the Supreme Court has sustained a variety of affirmative action plans and programs established by government. A majority of the justices have upheld education and employment opportunities being targeted to qualified minority and female candidates where there is a manifest imbalance of representation for that group and race or gender is one of several factors taken into account. But during the 1980s and 1990s the justices started striking down programs allowing greater equality of result. In Adarand Constructors v. Pena (1995), the Supreme Court held that any that government affirmative action policy using racial classifications as the basis for making decisions is subject to strict scrutiny. This meant that the justices would presume the policy to be unconstitutional unless narrowly tailored to further a compelling government interest of the highest order. The majority explained that affirmative action plans could no longer give preferences to less qualified persons to remedy past discrimination by society. Instead affirmative action plans had to be narrowly tailored to remedy actual discrimination that has occurred and then had to be terminated after the plan has been successful. It has become very difficult after the Adarand decision for government to take affirmative steps to equalize social, political, and economic opportunities for disadvantaged groups. Lower courts have overturned such policies because they were aimed at remedying past discrimination in general rather than actual discrimination in the case of a particular individual.

After Adarand and other decisions, a strong political movement emerged against affirmative action. The 1990s witnessed growing criticism from voters and officials about problems with preferential treatment and reverse discrimination. In 1995, the Regents of the University of California voted to eliminate the use of race or gender factors in employment, purchasing, contracting, or admissions. In 1996, the citizens of California voted overwhelmingly for Proposition 209 to amend the constitution forbid state agencies to discriminate against or grant preferential treatment to any individual or group on the basis of race, gender, color, ethnicity, or national origin in public employment, education, and contracting except where necessary to comply with federal guidelines. The people of Washington, Texas, Florida, and other states have also voted to abandon affirmative action policies. Public opinion seems to be that affirmative action has served its purpose and that government efforts to bring about equality of outcome on the basis of race or gender are unfair. Do affirmative action programs constitute reverse discrimination or serve to ameliorate against the lingering effects of discrimination? Would affirmative action produce greater equality for disadvantaged people if policies took socioeconomic status into account with the effect that the poor would be helped regardless of race, gender, and so on?