In my area, the min wage is somewhere around $15/hr. Anything less than 20% tip on top of that $15/hr is considered stingy. The restaurants that do a service charge instead of tipping add 22% and sometimes a 4% fee to pay for employee health insurance.
Anymore, we really only dine out for special occasions or a monthly visit to our favorite spot.
If tipped employees are just earning that standard minimum wage and nobody tips them, then they just get the minimum wage. I can see situations where they'd be pretty mad -- there are a lot of restaurants where tipped employees make more than the standard minimum wage.
All of that said, I believe that tipping is horseshit and should go away. But I can't protest it by refusing to tip unless I want to punish the wrong people.