Telling customers who criticize your company to take their business elsewhere is not defending the employees and it is not what any actual employer would do.
Most customer service companies train their people to respond to customer criticisms and provide them with a process to pass the information along. Some provide mechanisms for first point of contact employees to resolve issues.
I don't know of any company that allows their employees to tell a customer their business is not wanted solely based on criticism the customer might offer.
If you do, I'd like to know who.