Because I was raised by educated people, in a cosmopolitan (by Midwestern standards) environment, I leave a tip when eating in a restaurant. But so what if I didn't?
One of the defining characteristics of a tip is the fact that it's optional. If you'd rather not leave a tip, because the service wasn't any good, or because you can afford to eat out more often if you don't, you don't have you.
(Arguably, you should be allowed to leave a tip in the form of an actual tip, written on the receipt.)
You shouldn't have to sweat some trust fund baby on the Internets trying to lay a guilt trip on you, arguing that not tipping constitutes wage theft—when you're not even their employer!
Legally, I'm pretty sure that the restaurant is required to supplement the wait staff's tips, if the amount they receive for a shift comes to less than minimum wage. So arguably you're doing society a favor by not leaving a tip, thus forcing the greedy owner to pay his staff more. If he owns a restaurant, chances are he's got more money than you do. Certainly, he's got more money than I do.
If restaurant employees aren't aware that the owner is required to supplement their tips, because they don't speak English, or because they need at least $20 cash to buy some drugs, then that's a separate issue and not my concern.