I still see some businesses with a sign outside...
that reads, "This establishment reserves the right to refuse service to anyone."
Is that illegal? Obviously, such a policy can be abused like it was in the Jim Crow days when blacks were not allowed in many businesses. However, if a business owner must provide service for literally anyone, then there can be abuse of other customers. As an example, should a business be forced to provide service to someone who is violently drunk?