There would be bo problem is it was simply stated "You pay the restaurant for your food and pay 18% commission to the person who serves it to you"
Indeed. And I would then serve the food to myself and keep the 18%. As matter of fact, that's what I do - if I step into a [fast] food place I just buy food. I have arms and legs and I'm quite capable of carrying my purchase. I don't need to hire someone else to carry a tray for 10 yards.
I never give tips; but at the same time I never visit places where tips are expected. This way restaurant's people are happy, and I am happy. Perhaps they'd like to see me as a customer, but they need to change their ways for that and get rid of tips, like this:
I then look at the prices and make my decision. I pay what the number says, and that's it. I hate uncertainty and fuzziness.