Why did Justice Henry Billings Brown conclude that racial separation did not violate legal equality?

In the majority opinion for Plessy v. Ferguson (1896), Justice Henry Billings Brown concluded that racial segregation did not violate legal equality by drawing a sharp distinction between legal equality and social equality.1

Brown argued that the Fourteenth Amendment was intended to secure only the former, not the latter. He maintained that the Separate Car Act respected legal equality because it required that accommodations for both races be equal and because he believed that segregation did not, by itself, imply the legal inferiority of any race.1

Conversely, Brown asserted that social equality—which he characterized as the "commingling" of races—could not be created by law, as it relied on the "natural affinities" and voluntary choices of individuals. He further justified the ruling by stating that the law was a "reasonable" exercise of the state's police power to maintain "public peace and good order," arguing that legislation was powerless to eradicate racial instincts. This doctrine of separate but equal provided constitutional sanction for segregation until it was eventually overturned by the Supreme Court in 1954.12