As a person who works in the food and beverage industry, I can confidently say, that tipping is a requirement, unless you enjoy endorsing slave labor. Most states have a reduced wage for waiters and bartenders. For example, the state in which in reside, Oklahoma pays servers 2.13/hr. They are depending on your generosity and common sense to provide for their families.
If you can not afford to tip, you most likely cannot afford to go out to dinner.