So it's not unfair not because it's a common business practice but because it's a common business practice? Are you even trying to make sense?
If it's a common business practice, it is fair until it's not. Prove unfairness or abuse, and you are looking at discrimination; don't, and discrimination hasn't even entered the picture.
BTW: segregated seating on buses by race was a "common business practice" at one point, too, and even now, offering "preferred seating" at the front is common on many airlines.
But people were treated unfairly because of it, hence it was a common business practice that was discriminatory. The unfairness--the discrimination--in this case, was reflected in
how people felt. If you honestly feel that as an atheist you are discriminated against by virtue of a religious group getting a discount on Sunday, then you should have to explain
why you do not also feel discriminated against by virtue of children getting a discount on Tuesday. If it comes down to the particular "dividing lines" mentioned in the Civil Rights Act, then you are basing your hurt feelings on the law rather than discrimination or civil rights.
And that's okay, but it's not an argument for discrimination or about civil rights.
If
no one felt they were treated unfairly by having to sit at the back of the bus, would we have a law about it? Would anyone even mind?
It was based on the contradictory rule that you came up with: that having a "standard" price to which a discount is applied for some customers is okay because the remaining customers can still get the "standard" price, despite the fact that when some customers have access to a discounted price, the "standard" price can no longer be considered standard.
On the contrary, I am the one who pointed out that having a discount doesn't affect the actual listed price of the meal.
Point out to me the unfairness of a discount to kids on Tuesdays, or to the birthday boy on his birthday. Tell me about hurt feelings, humiliation and being made to feel less than human because of it. Then I might believe you.