I’m not sure it was sarcasim. I don’t think it was. I remember the first time I heard this point, and while instinctivly disagreeing with it - it does makes sense.
If the owner of a private business (Woolworths or a coffee store) does not want to serve someone - based on whatever, why are they not allowed to do that? While I wouldn’t agree with the owner to not allow blacks - why is that not his right? (Seems dumb though to turn away customers though).
On a Federal and State level that is a whole different thing (discrimination).
That is why you never discuss Politics or Religion while operating a Retail Establishment. When you count the Receipts at the end of the day, you don't know or care which bills came from which customers.