The facts of this 1883 case are simple, and the Supreme Court's decision abhorrent to any modern person. Tony Pace was a black man living in Alabama, dating a white woman. Unfortunately, Alabama's anti-miscegenation laws forbade sexual relations or marriage between blacks and whites. Lower courts' logical contortions to justify the law were remarkable. For example, Pace and his white girlfriend were charged with adultery, since they were found living together without being married. However, state law made it illegal for them to get married. Alabama's Supreme Court decided that the law was not discriminatory because it applied equally to both blacks and whites. That is, it was illegal for a black person to marry a white person, but it was equally illegal for a white person to marry a black person. The case was appealed all the way to the U.S. Supreme Court, which determined that protecting the institution of marriage was a valid interest for the state, and that the threat of interracial relationships would cause serious harm to "white marriages." Therefore, the law couldn't be ruled unconstitutional.
What's truly sad is that the case wasn't overturned until 1967, and that several lower courts issued rulings based on the same blatantly racist principles in place more than 80 years prior. In Loving v. Virginia, the Supreme Court finally ruled unanimously that such laws had no legal standing and were merely state-sponsored racism. They overthrew a Virginia law against interracial marriage and rendered all other such laws invalid.