What circumstances might lead to people's rights being denied in a direct democracy

Direct democracy is when everyone in a country votes on something. People's rights might be denied because it would be a tyrannical rule of the majority. For example, there's only 15% African-Americans in the US. If the 85% Caucasian population decided to vote something that was against the rights of the African-Americans, they wouldn't be able to oppose this because they would be a minority.