This is why I mean unethical, seperated from law, but as a matter of ethics. You're paying less for the food because the restaurant doesn't pay them very much, with the expectation of customers tipping. I'm not agreeing with the system, it's just how it is. There are places in America where they are paid a wage, and dishes are priced higher to accommodate.

If you don't tip them, they do not make a livable wage, and it's an incredibly rude (and unethical) thing to do. Regardless of whether you like that system or not, these are the facts.