The argument that you should always tip food service ~20% is generally based on the claim that "quality signal mechanism" is not actually the intent of the tipp

The argument that you should always tip food service ~20% is generally based on the claim that "quality signal mechanism" is not actually the intent of the tipping system, but merely an excuse (that was perhaps true at some point in the past) to justify legally paying workers low wages and artificially reducing the sticker price of food.