Greg Beato supplies one:
These days, the idea of not tipping is almost as impossible to comprehend as the idea of paying for news. Who does that? Crazy people? Criminals? ... Things were much different a century ago. Between 1909 and 1926, six states passed laws that made tipping illegal. Restaurants posted “Tipping is not American!” signs in their dining rooms. In a republic where the waiter was the political and moral equal of the millionaire factory owner, each endowed with the same essential rights and freedoms, tipping was seen as “a hangover of Old World flunkeyism” as one New York Times editorial opined. It divided a classless society into servant and served.