I don't believe you are giving nearly enough credit to the civil rights movement or its ongoing efforts. Racism existed in various forms for hundreds (thousands, if we go back to Aristotle) of years. It is a human institution, like slavery or marriage, both of which have taken concerted effort and time to end or change.
The "free market of ideas" only works if you assume everyone is a rational actor judging ideas on their direct merits. That simply is not the case.
The "free market of ideas" only works if you assume everyone is a rational actor judging ideas on their direct merits. That simply is not the case.