I'm not sure that has to do with privacy and more like "help us avoid paying income taxes." No one denies that cash is completely anonymous, but that's not the intent here. This is coming from a huge advocate for privacy, but to me this is a stretch.
I agree with the idea and I don't have this reaction else where but when I see the cash only signs in food places it just makes me jump to tax evasion. Don't know why it's only food places that give me that feeling.
I was wondering... how much does a credit company know if I pay with my cc? Do they know every detail of my lunch menu? If so, that does have something to do with privacy, I'm not very comfortable. If they just know the total amount I pay, then I wouldn't mind too much, though.