And disallowed from refusing service to people in many other situations, just as they are disallowed from stirring shit into food. That we tell businesses what they can and can't do is a fact, so it's:

1) useful to discuss whether or not we should allow or disallow things, and

2) useless to discuss whether private business can do whatever they want because they are private businesses. The answer to that is that private businesses can't do what they want, instead they're allowed to do what we haven't told them they can't do, and must do what we've told them they must do.