History has plenty of examples where it works, however in many other cases the policy just limits those trying it. Most people don't care enough about your prejudice when they can get a better deal and suddenly the out group becomes normal business partners.
No, nothing offered upthread suggested that. First of all because it didn't refer to merely having a shareholder of a particular ethnicity, but more critically because it didn't suggest it was illegal to refuse to do business with a company that happened to have a major shareholder or board member of a particular race or ethnicity but that it was illegal for a business to refuse to do business because of the race/ethnicity of some party holding a specified role ownership/management role within the target firm.
GP was disputing your characterization of the example as absurd, nothing more.
I don’t know your gender, race, ethnicity, religion, or country of origin, but I can guarantee someone you’re going to have issues doing business because of discrimination. Saying X in not an issue in a country where X is protected/prohibited/regulated etc is a very week argument for getting rid of the associated laws.