The problem with racist customers is that they are harassing your other customers and driving them away. My boyfriend gets this all the time: racist customers harass my boyfriend, a well behaved customer, and frequently the management of the business sides with the racist customers, blaming him for causing trouble for the business. This causes him to take his business elsewhere.
It’s very hard to talk with another person while they are screaming at or insulting one of your customers. You need to get them out of your business and away from their target.
In such environments, it is important to take a strong stand against racist customers and racist behavior, lest they drive away other customers that generate revenue. You also need to routinely vet your staff and fire racist employees promptly.