You don't. However, not tipping in the current system makes you an asshole. In a perfect world tipping wouldn't be required, but we don't live there right now,

You don't. However, not tipping in the current system makes you an asshole. In a perfect world tipping wouldn't be required, but we don't live there right now, and until then all you're doing by not tipping is hitting some working class person in their pocketbook.