It turned out, there weren't many market consequences for excluding black people in the American South because they lacked purchasing power (on account of the years of oppression leading to wildly-unequal amounts of resource ownership). There was just suffering and exclusion.

History suggests the market can't solve everything. History also suggests the majority is not always right, which is why the US government is structured as a system of checks and balances and not a simpler-to-implement mobocracy.

Are you arguing that ending Constitutional protections for minorities to freely associate was necessary to preserve the freedom of minorities?

Nobody ended those freedoms categorically. Those freedoms still exist in the context of personal association and most group associations.

But (like any business owner) if a minority business owner wants to incorporate and exchange money with the public for goods and/or services, their rights are curtailed like everybody else's are regarding who they may not refuse service to. For example, a black business owner isn't allowed to kick white people out. They are allowed to kick Klansmen out (as per federal law; states may place additional restrictions).

It is the nature of societies that we give up some rights to protect others. The law is one long, ongoing conversation on what that trade-off looks like. And in the specific case, I'm of the opinion that we tried it the other way (refraining from curtailing the right for a business to refuse service universally) for at least a hundred years and found that it didn't make a good society.