Why is it inherently unfair to put the civil rights of minorities to a public vote?

Even though in 1967 the Supreme Court declared anti-miscegenation laws unconstitutional, by 1970, twelve states, mostly in the Bible Belt, still had unenforceable miscegenation laws still on their books. Here's just one example:

The last one wasn’t removed until November of 2000, in Alabama. And strangely, it was done by a ballot referendum. In November 2000, after a statewide vote in a special election to finally and officially end Alabama’s miscegenation law, they became the last state to overturn a law that was an ugly reminder of America's past - a ban on interracial marriage. Yet in the one-time home of Martin Luther King Jr. and Rosa Parks, and 33 years after the U.S. Supreme Court declared anti-miscegenation laws unconstitutional….40 PERCENT OF VOTERS WANTED TO KEEP THE BAN! Millions of people STILL saw a necessity for a law to prohibit blacks and whites from marrying each other!

“In view of the constitution, in the eye of the law, there is in this country no superior, dominant, ruling class of citizens. There is no caste here. Our constitution is color-blind, and neither knows nor tolerates classes among citizens. In respect of civil rights, all citizens are equal before the law. The humblest is the peer of the most powerful.” “It is hostile to both the spirit and letter of the Constitution...to place in a condition of legal inferiority a large body of American citizens."

- United States Supreme Court Justice John Marshall Harlan, -1896