A pretty decent public school education. I'm not going to be able to quote you sources because I didn't write down cites for four years of high school. But like I said, not working from the same collection of facts. I wonder what your sources are, because you're pretty off-the-bead from the commonly-taught knowledge of US history in the US (and seem to be basing a lot of beliefs about how America should run its affairs on that information).
Black people were, obviously, able to work. Sharecropping came in right after slavery left. We're not talking about work in general; we're talking about work in a corporate environment. American firms mostly simply did not hire black people until the law forced them to (especially to skilled-labor jobs). And the evidence that this restriction was primarily based on racial prejudice is overwhelming.
> nobody is entitled to a loan
Hey, you're right! Although as of the Equal Credit Opportunity Act, borrowers are entitled to have their skin color ignored when they request a loan.
In addition, nobody is entitled to own a business. They can certainly work for themselves (being a contractor is a thing, gig economy is a thing, short-term work is a thing), but the privilege of incorporating, of creating the legal fiction of a "company," of having one's personal assets and fortunes divorced from the errors and risks of one's corporation... That's a privilege that carries several societal obligations. Nobody is owed that legal protection, especially if they aren't interested in abiding by the law of the land.
I'm operating under the assumption that you don't have an issue with the notion that being a company owner requires one to be responsible for tax law compliance, or EPA toxic-waste compliance, or securities / exchange reporting compliance. Is there something special about equal opportunity compliance that you take issue with? If not, suffice to know the government's right to impose it extends from the same right that imposes EPA law and tax law.