Couple of issues here. First, these are not the same. A business is offering a service to the public and then denying people who walk in, whereas a customer is simply deciding which offer he takes. This is where the stark differences only begin.
a customer can, unless the product is in some special regulated category, be anyone. In fact, even if its regulated, most criteria we are concerned with here could never really be used in licensing them, so its kind of irrelevant. Whereas a shop owner is someone who sought out and obtained a charter from the government which grants him limited liability, so he is not fully responsible for what he does in the course of his business.
This right here is the point where, in my eyes, the whole game changes. A company is a chartered entity authorized by the government. If he was a private individual servicing people out of his private home, or he was running a private members-only club.... I wouldn't argue at all, this would be quite unfair. I fully support the right of organizations like the KKK setting up members only clubs and selling whatever they want (short of slaves) to their own members.
However, when these people chartered their businesses and opened public businesses, they do so with benefits like limited liability which, I have no problem with the chartering entitiy putting restrictions on if those charters.