Earlier quoted context omitted.
Why would that argument not apply to "It's 1960, and I don't want to seat black customers at my fancy restaurant because it's statistically likely to be less profitable than seating white customers"?
Because black customers pay the same prices and do not require additional accommodations. It would apply if the restaurateur was required to maintain separate dining rooms for whites and blacks or additional water fountains.
If you have more customers trying to make reservations than tables to seat them, it is economically rational to seat the customers most likely to buy your more expensive items. We decided (correctly, IMO) that it is more important for society to fight entrenched racism than to enable business owners to make that particular locally-rational economic decision.