The customer would be nice and friendly and never complain about the service but then just walk out of the restaurant without leaving a tip. It happens to every waiter.

Isn't that what the state's minimum-wage law is all about? Doesn't it mandate that employers pay workers a state-established minimum wage to ensure that employers don't exploit them by paying them sub-minimum wages?

Why shouldn't the state do the same by enacting a minimum-tipping law, one that requires restaurant customers to pay waiters a minimum 15 percent tip? Given that the state protects workers from the possibility of exploitation with a minimum-wage law, why shouldn't it protect waiters from the possibility of exploitation from restaurant customers?

The reason is freedom. Most Americans don't want the state to be involved in tipping. They understand that the matter of tipping is simply none of the state's business. They want the matter to be handled by the free market, i.e. , a market that is free of governmental interference or involvement.