I don't mean to demean waiters, but in the context of my reply, I'm trying to point out that they are not business owners, and I certainly do not contract with them simply by having a meal they happened to serve.
If a waiter gives you bad service, do you go back to the restaurant?
If the waiter makes your meal a much more enjoyable experience, would you be likely to go back to the restaurant?
It seems to me like there is a social contract involved in that interaction. A waiter who encourages you to return helps the restaurant, but also provided a service to you (a pleasant meal).
As such, the gratuity is a reflection from you back to the waiter as to how much you valued his work.
Waiters who encourage more patronage are not just working for the restaurant, they are providing a service to the diner beyond “just serving food”. A waiter can make or break a nice night out, and I think it is horribly elitist to say “they are just doing their job” and “Waiters are hired flunkies doing low-end labor”.
Well, in America, you do.
By virtue of waitstaff being exempted from minimum wage laws, you, as a customer are assuming some payment for their services.
Now you know what all that cussing was about when you left a US restaurant without tipping. The poor sap had to cough up income tax on 8% of your bill, also. It's almost like you stole his services.